Rupture dynamics with energy loss outside the slip zone

USGS Publications Warehouse

Andrews, D.J.

2005-01-01

Energy loss in a fault damage zone, outside the slip zone, contributes to the fracture energy that determines rupture velocity of an earthquake. A nonelastic two-dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a Coulomb yield condition. In a mode 2 crack-like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point, Coulomb yielding occurs on the extensional side of the fault. Plastic strain is distributed with uniform magnitude along the fault, and it has a thickness normal to the fault proportional to propagation distance. Energy loss off the fault is also proportional to propagation distance, and it can become much larger than energy loss on the fault specified by the fault constitutive relation. The slip velocity function could be produced in an equivalent elastic problem by a slip-weakening friction law with breakdown slip Dc increasing with distance. Fracture energy G and equivalent Dc will be different in ruptures with different initiation points and stress drops, so they are not constitutive properties; they are determined by the dynamic solution that arrives at a particular point. Peak slip velocity is, however, a property of a fault location. Nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium.

Fault Zone Imaging from Correlations of Aftershock Waveforms

NASA Astrophysics Data System (ADS)

Hillers, Gregor; Campillo, Michel

2018-03-01

We image an active fault zone environment using cross correlations of 154 15 s long 1992 Landers earthquake aftershock seismograms recorded along a line array. A group velocity and phase velocity dispersion analysis of the reconstructed Rayleigh waves and Love waves yields shear wave velocity images of the top 100 m along the 800 m long array that consists of 22 three component stations. Estimates of the position, width, and seismic velocity of a low-velocity zone are in good agreement with the findings of previous fault zone trapped waves studies. Our preferred solution indicates the zone is offset from the surface break to the east, 100-200 m wide, and characterized by a 30% velocity reduction. Imaging in the 2-6 Hz range resolves further a high-velocity body of similar width to the west of the fault break. Symmetry and shape of zero-lag correlation fields or focal spots indicate a frequency and position dependent wavefield composition. At frequencies greater than 4 Hz surface wave propagation dominates, whereas at lower frequencies the correlation field also exhibits signatures of body waves that likely interact with the high-velocity zone. The polarization and late arrival times of coherent wavefronts observed above the low-velocity zone indicate reflections associated with velocity contrasts in the fault zone environment. Our study highlights the utility of the high-frequency correlation wavefield obtained from records of local and regional seismicity. The approach does not depend on knowledge of earthquake source parameters, which suggests the method can return images quickly during aftershock campaigns to guide network updates for optimal coverage of interesting geological features.

The effect of segmented fault zones on earthquake rupture propagation and termination

NASA Astrophysics Data System (ADS)

Huang, Y.

2017-12-01

A fundamental question in earthquake source physics is what can control the nucleation and termination of an earthquake rupture. Besides stress heterogeneities and variations in frictional properties, damaged fault zones (DFZs) that surround major strike-slip faults can contribute significantly to earthquake rupture propagation. Previous earthquake rupture simulations usually characterize DFZs as several-hundred-meter-wide layers with lower seismic velocities than host rocks, and find earthquake ruptures in DFZs can exhibit slip pulses and oscillating rupture speeds that ultimately enhance high-frequency ground motions. However, real DFZs are more complex than the uniform low-velocity structures, and show along-strike variations of damages that may be correlated with historical earthquake ruptures. These segmented structures can either prohibit or assist rupture propagation and significantly affect the final sizes of earthquakes. For example, recent dense array data recorded at the San Jacinto fault zone suggests the existence of three prominent DFZs across the Anza seismic gap and the south section of the Clark branch, while no prominent DFZs were identified near the ends of the Anza seismic gap. To better understand earthquake rupture in segmented fault zones, we will present dynamic rupture simulations that calculate the time-varying rupture process physically by considering the interactions between fault stresses, fault frictional properties, and material heterogeneities. We will show that whether an earthquake rupture can break through the intact rock outside the DFZ depend on the nucleation size of the earthquake and the rupture propagation distance in the DFZ. Moreover, material properties of the DFZ, stress conditions along the fault, and friction properties of the fault also have a critical impact on rupture propagation and termination. We will also present scenarios of San Jacinto earthquake ruptures and show the parameter space that is favorable for rupture propagation through the Anza seismic gap. Our results suggest that a priori knowledge of properties of segmented fault zones is of great importance for predicting sizes of future large earthquakes on major faults.

Propagation of gaseous detonation waves in a spatially inhomogeneous reactive medium

NASA Astrophysics Data System (ADS)

Mi, XiaoCheng; Higgins, Andrew J.; Ng, Hoi Dick; Kiyanda, Charles B.; Nikiforakis, Nikolaos

2017-05-01

Detonation propagation in a compressible medium wherein the energy release has been made spatially inhomogeneous is examined via numerical simulation. The inhomogeneity is introduced via step functions in the reaction progress variable, with the local value of energy release correspondingly increased so as to maintain the same average energy density in the medium and thus a constant Chapman-Jouguet (CJ) detonation velocity. A one-step Arrhenius rate governs the rate of energy release in the reactive zones. The resulting dynamics of a detonation propagating in such systems with one-dimensional layers and two-dimensional squares are simulated using a Godunov-type finite-volume scheme. The resulting wave dynamics are analyzed by computing the average wave velocity and one-dimensional averaged wave structure. In the case of sufficiently inhomogeneous media wherein the spacing between reactive zones is greater than the inherent reaction zone length, average wave speeds significantly greater than the corresponding CJ speed of the homogenized medium are obtained. If the shock transit time between reactive zones is less than the reaction time scale, then the classical CJ detonation velocity is recovered. The spatiotemporal averaged structure of the waves in these systems is analyzed via a Favre-averaging technique, with terms associated with the thermal and mechanical fluctuations being explicitly computed. The analysis of the averaged wave structure identifies the super-CJ detonations as weak detonations owing to the existence of mechanical nonequilibrium at the effective sonic point embedded within the wave structure. The correspondence of the super-CJ behavior identified in this study with real detonation phenomena that may be observed in experiments is discussed.

Optical wave distortion at perturbations of air density near aircrafts with subsonic velocities

NASA Astrophysics Data System (ADS)

Banakh, V. A.; Sukharev, A. A.

2017-11-01

The mean intensity, intensity fluctuations, and regular and random displacements of optical beams propagating through a zone of increased density formed at subsonic airflow about a turret in the turbulent atmosphere have been analyzed. It has been shown that the presence of perturbations around a turret due to the subsonic velocity of aircraft affects slightly the studied characteristics of the beam. Data illustrating changes in the studied beam characteristics for paths of different geometry and different turbulent conditions of radiation propagation are presented.

Crustal Structure of the Middle East from Regional Seismic Studies

NASA Astrophysics Data System (ADS)

Gritto, Roland; Sibol, Matthew; Caron, Pierre; Ghalib, Hafidh; Chen, Youlin

2010-05-01

We present results of crustal studies obtained with seismic data from the Northern Iraq Seismic Network (NISN). NISN has operated ten broadband stations in north-eastern Iraq since late 2005. This network was supplemented by the five-element broadband Iraq Seismic Array (KSIRS) in 2007. More recently, the former Iraq Seismic Network (ISN), destroyed during the war with Iran, was reestablished with the deployment of six broadband stations throughout Iraq. The aim of the present study is to derive models of the local and regional crustal structure of the Middle East, including Eastern Turkey, Iraq and Iran. To achieve this goal, we derive crustal velocity models using receiver function, surface wave and body wave analyses. These refined velocity models will eventually be used to obtain accurate hypocenter locations and event focal mechanisms. Our analysis of preliminary hypocenter locations produced a clearer picture of the seismicity associated with the tectonics of the region. The largest seismicity rate is confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases in the Bandar Abbas region again. Additionally, the rift zones in the Red Sea and the Gulf of Aden are clearly demarked by high seismicity rates. Surface wave velocity analysis resulted in a clear demarcation of the tectonic features in the region. The Arabian shield, Zagros thrust zone and the Red Sea are apparent through distinct velocity distributions separating them from each other. Furthermore, the shear wave velocity of the crust in North Iraq appears to be 10% higher than that of the Iranian plateau. The velocity anomaly of the Zagros mountains appears to be present into the upper mantle beyond the resolving limit of our model. Analysis of waveform data for obstructed pathways indicates clear propagation paths from the west or south-west across the Arabian shield as well as from the north and east into NISN. Phases including Pn, Pg, Sn, Lg, as well as LR are clearly observed on these seismograms. In contrast, blockage or attenuation of Pg and Sg-wave energy is observed for propagation paths across the Zagros-Makran zone from the south, while Pn and Sn phases are not affected. These findings are in support of earlier tectonic models that suggested the existence of multiple parallel listric faults splitting off the main Zagros fault zone in westerly direction. These faults appear to attenuate the crustal phases while the refracted phases, propagating across the mantle lid, remain unaffected. Azimuthal phase count and velocity analyses of body waves support the findings of blockage by the Zagros-Makran zone as well as higher shear wave velocities for the crust in Northern Iraq. In combination with receiver function and refraction studies, our first structural model of the crust beneath north-eastern Iraq indicates crustal depth of 40-45 km for the foothills, which increases to 45-50 km below the core of the Zagros-Bitlis zone.

Model of the Streamer Zone of a Leader

NASA Astrophysics Data System (ADS)

Milikh, G. M.; Raina, A.; Shneider, M.; Likhanskii, A.; George, A.

2015-12-01

Developed leaders represent highly conductive plasma channels, continuously emitting a fan of streamers, termed the streamer zone. The tip moves at a speed much slower than that of individual streamers. A huge number of short-lived streamers in the corona generate the space charge field required to maintain the streamer propagation. A critical issue is the conversion from the streamer to leader phase [Da Silva and Pasko, 2013]. The objective of this paper is to present simulations of the formation and propagation of the streamer zone of a leader. In these simulations we generated a group of streamers that propagate in a discharge gap while they interact with each other. We use the modified numerical model [Likhanskii et al., 2007] developed to simulate discharge plasma actuators driven by nanosecond pulses. The model uses 2D rectangular computational box, and the discharge gap is filled with the air at normal conditions. Furthermore the model considers electrons, positive and negative ions. The plasma kinetics and interaction with neutral molecules is modeled in a drift-diffusion approximation [Likhanskii et al., 2007]. The electric field and potential are related to the density of charged species according to the Poisson equation. The latter was solved by the successive over-relaxation method. It is shown that interaction between the streamers significantly reduces their propagation velocity. Furthermore the streamer velocity depends on the distance between the streamers. The smaller is that distance the stronger is the suppression of the streamer velocity. This explains why the leader, which consists of many streamers, is much slower than a single streamer formed in the same discharge gap. C.L. Da Silva and V.P. Pasko, J. Geophys. Res.: Atmospheres, 118, 1-30, 2013 A.V. Likhanskii et al., Phys. Plasmas, 14, 073501, 2007.

Strain-dependent Damage Evolution and Velocity Reduction in Fault Zones Induced by Earthquake Rupture

NASA Astrophysics Data System (ADS)

Zhong, J.; Duan, B.

2009-12-01

Low-velocity fault zones (LVFZs) with reduced seismic velocities relative to the surrounding wall rocks are widely observed around active faults. The presence of such a zone will affect rupture propagation, near-field ground motion, and off-fault damage in subsequent earth-quakes. In this study, we quantify the reduction of seismic velocities caused by dynamic rup-ture on a 2D planar fault surrounded by a low-velocity fault zone. First, we implement the damage rheology (Lyakhovsky et al. 1997) in EQdyna (Duan and Oglesby 2006), an explicit dynamic finite element code. We further extend this damage rheology model to include the dependence of strains on crack density. Then, we quantify off-fault continuum damage distribution and velocity reduction induced by earthquake rupture with the presence of a preexisting LVFZ. We find that the presence of a LVFZ affects the tempo-spatial distribu-tions of off-fault damage. Because lack of constraint in some damage parameters, we further investigate the relationship between velocity reduction and these damage prameters by a large suite of numerical simulations. Slip velocity, slip, and near-field ground motions computed from damage rheology are also compared with those from off-fault elastic or elastoplastic responses. We find that the reduction in elastic moduli during dynamic rupture has profound impact on these quantities.

Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone

USGS Publications Warehouse

Hough, S.E.; Ben-Zion, Y.; Leary, P.

1994-01-01

Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50.

Welding induced residual stress evaluation using laser-generated Rayleigh waves

NASA Astrophysics Data System (ADS)

Ye, Chong; Zhou, Yuanlai; Reddy, Vishnu V. B.; Mebane, Aaron; Ume, I. Charles

2018-04-01

Welding induced residual stress could affect the dimensional stability, fatigue life, and chemical resistance of the weld joints. Ultrasonic method serves as an important non-destructive tool for the residual stress evaluation due to its easy implementation, low cost and wide application to different materials. Residual stress would result in the ultrasonic wave velocity variation, which is the so called acoustoelastic effect. In this paper, Laser/EMAT ultrasonic technique was proposed to experimentally study the relative velocity variation ΔV/V of Rayleigh wave, which has the potential to evaluate surface/subsurface longitudinal residual stress developed during the Gas Metal Arc Welding process. Broad band ultrasonic waves were excited by pulsed Q-Switched Nd: YAG laser. An electromagnetic acoustic transducer (EMAT) attached to the welded plates was used to capture the Rayleigh wave signals propagating along the weld seam direction. Different time of flight measurements were conducted by varying the distance between the weld seam and Rayleigh wave propagating path in the range of 0 to 45 mm. The maximum relative velocity difference was found on the weld seam. With the increasing distance away from the weld seam, the relative velocity difference sharply decreased to negative value. With further increase in distance, the relative velocity difference slowly increased and approached zero. The distribution of relative velocity variations indicates that tensile stress appears in the melted zone as it becomes compressive near the heat-affected zone.

Rupture models with dynamically determined breakdown displacement

USGS Publications Warehouse

Andrews, D.J.

2004-01-01

The critical breakdown displacement, Dc, in which friction drops to its sliding value, can be made dependent on event size by specifying friction to be a function of variables other than slip. Two such friction laws are examined here. The first is designed to achieve accuracy and smoothness in discrete numerical calculations. Consistent resolution throughout an evolving rupture is achieved by specifying friction as a function of elapsed time after peak stress is reached. Such a time-weakening model produces Dc and fracture energy proportional to the square root of distance rupture has propagated in the case of uniform stress drop. The second friction law is more physically motivated. Energy loss in a damage zone outside the slip zone has the effect of increasing Dc and limiting peak slip velocity (Andrews, 1976). This article demonstrates a converse effect, that artificially limiting slip velocity on a fault in an elastic medium has a toughening effect, increasing fracture energy and Dc proportionally to rupture propagation distance in the case of uniform stress drop. Both the time-weakening and the velocity-toughening models can be used in calculations with heterogeneous stress drop.

The Propagation of a Surge Front on Bering Glacier, Alaska, 2001-2011

NASA Technical Reports Server (NTRS)

Turrin, James; Forster, Richard R.; Larsen, Chris; Sauber, Jeanne

2013-01-01

Bering Glacier, Alaska, USA, has a 20 year surge cycle, with its most recent surge reaching the terminus in 2011. To study this most recent activity a time series of ice velocity maps was produced by applying optical feature-tracking methods to Landsat-7 ETM+ imagery spanning 2001-11. The velocity maps show a yearly increase in ice surface velocity associated with the down-glacier movement of a surge front. In 2008/09 the maximum ice surface velocity was 1.5 plus or minus 0.017 kilometers per a in the mid-ablation zone, which decreased to 1.2 plus or minus 0.015 kilometers per a in 2009/10 in the lower ablation zone, and then increased to nearly 4.4 plus or minus 0.03 kilometers per a in summer 2011 when the surge front reached the glacier terminus. The surge front propagated down-glacier as a kinematic wave at an average rate of 4.4 plus or minus 2.0 kilometers per a between September 2002 and April 2009, then accelerated to 13.9 plus or minus 2.0 kilometers per a as it entered the piedmont lobe between April 2009 and September 2010. Thewave seems to have initiated near the confluence of Bering Glacier and Bagley Ice Valley as early as 2001, and the surge was triggered in 2008 further down-glacier in the mid-ablation zone after the wave passed an ice reservoir area.

Generalized Pseudo-Reaction Zone Model for Non-Ideal Explosives

NASA Astrophysics Data System (ADS)

Wescott, B. L.

2007-12-01

The pseudo-reaction zone model was proposed to improve engineering scale simulations with high explosives that have a slow reaction component. In this work an extension of the pseudo-reaction zone model is developed for non-ideal explosives that propagate well below the steady-planar Chapman-Jouguet velocity. A programmed burn method utilizing Detonation Shock Dynamics (DSD) and a detonation velocity dependent pseudo-reaction rate has been developed for non-ideal explosives and applied to the explosive mixture of ammonium nitrate and fuel oil (ANFO). The pseudo-reaction rate is calibrated to the experimentally obtained normal detonation velocity—shock curvature relation. Cylinder test simulations predict the proper expansion to within 1% even though significant reaction occurs as the cylinder expands.

DYNAMIC PLANE-STRAIN SHEAR RUPTURE WITH A SLIP-WEAKENING FRICTION LAW CALCULATED BY A BOUNDARY INTEGRAL METHOD.

USGS Publications Warehouse

Andrews, D.J.

1985-01-01

A numerical boundary integral method, relating slip and traction on a plane in an elastic medium by convolution with a discretized Green function, can be linked to a slip-dependent friction law on the fault plane. Such a method is developed here in two-dimensional plane-strain geometry. Spontaneous plane-strain shear ruptures can make a transition from sub-Rayleigh to near-P propagation velocity. Results from the boundary integral method agree with earlier results from a finite difference method on the location of this transition in parameter space. The methods differ in their prediction of rupture velocity following the transition. The trailing edge of the cohesive zone propagates at the P-wave velocity after the transition in the boundary integral calculations. Refs.

Ignitable heterogeneous stratified structure for the propagation of an internal exothermic chemical reaction along an expanding wavefront and method of making same

DOEpatents

Barbee, T.W. Jr.; Weihs, T.

1996-07-23

A multilayer structure has a selectable, (1) propagating reaction front velocity V, (2) reaction initiation temperature attained by application of external energy, and (3) amount of energy delivered by a reaction of alternating unreacted layers of the multilayer structure. Because V is selectable and controllable, a variety of different applications for the multilayer structures are possible, including but not limited to their use as igniters, in joining applications, in fabrication of new materials, as smart materials and in medical applications and devices. The multilayer structure has a period D, and an energy release rate constant K. Two or more alternating unreacted layers are made of different materials and separated by reacted zones. The period D is equal to a sum of the widths of each single alternating reaction layer of a particular material, and also includes a sum of reacted zone widths, t{sub i}, in the period D. The multilayer structure has a selectable propagating reaction front velocity V, where V=K(1/D{sup n}){times}[1-(t{sub i}/D)] and n is about 0.8 to 1.2. 8 figs.

Ignitable heterogeneous stratified structure for the propagation of an internal exothermic chemical reaction along an expanding wavefront and method of making same

DOEpatents

Barbee, Jr., Troy W.; Weihs, Timothy

1996-01-01

A multilayer structure has a selectable, (i) propagating reaction front velocity V, (ii) reaction initiation temperature attained by application of external energy and (iii) amount of energy delivered by a reaction of alternating unreacted layers of the multilayer structure. Because V is selectable and controllable, a variety of different applications for the multilayer structures are possible, including but not limited to their use as ignitors, in joining applications, in fabrication of new materials, as smart materials and in medical applications and devices. The multilayer structure has a period D, and an energy release rate constant K. Two or more alternating unreacted layers are made of different materials and separated by reacted zones. The period D is equal to a sum of the widths of each single alternating reaction layer of a particular material, and also includes a sum of reacted zone widths, t.sub.i, in the period D. The multilayer structure has a selectable propagating reaction front velocity V, where V=K(1/D.sup.n).times.[1-(t.sub.i /D)] and n is about 0.8 to 1.2.

ZnO films on /001/-cut (110)-propagating GaAs substrates for surface acoustic wave device applications

NASA Technical Reports Server (NTRS)

Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei; Kim, Yoonkee; Hunt, William D.

1995-01-01

A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

Elastic Properties of Subduction Zone Materials in the Large Shallow Slip Environment for the Tohoku 2011 Earthquake: Laboratory data from JFAST Core Samples

NASA Astrophysics Data System (ADS)

Jeppson, T.; Tobin, H. J.

2014-12-01

The 11 March 2011 Tohoku-Oki earthquake (Mw=9.0) produced large displacements of ~50 meters near the Japan Trench. In order to understand earthquake propagation and slip stabilization in this environment, quantitative values of the real elastic properties of fault zones and their surrounding wall rock material is crucial. Because elastic and mechanical properties of faults and wallrocks are controlling factors in fault strength, earthquake generation and propagation, and slip stabilization, an understanding of these properties and their depth dependence is essential to understanding and accurately modeling earthquake rupture. In particular, quantitatively measured S-wave speeds, needed for estimation of elastic properties, are scarce in the literature. We report laboratory ultrasonic velocity measurements performed at elevated pressures, as well as the calculated dynamic elastic moduli, for samples of the rock surrounding the Tohoku earthquake principal fault zone recovered by drilling during IODP Expedition 343, Japan Trench Fast Drilling Project (JFAST). We performed measurements on five samples of gray mudstone from the hanging wall and one sample of underthrust brown mudstone from the footwall. We find P- and S-wave velocities of 2.0 to 2.4 km/s and 0.7 to 1.0 km/s, respectively, at 5 MPa effective pressure. At the same effective pressure, the hanging wall samples have shear moduli ranging from 1.4 to 2.2 GPa and the footwall sample has a shear modulus of 1.0 GPa. While these values are perhaps not surprising for shallow, clay-rich subduction zone sediments, they are substantially lower than the 30 GPa commonly assumed for rigidity in earthquake rupture and propagation models [e.g., Ide et al., 1993; Liu and Rice, 2005; Loveless and Meade, 2011]. In order to better understand the elastic properties of shallow subduction zone sediments, our measurements from the Japan Trench are compared to similar shallow drill core samples from the Nankai Trough, Costa Rica, Cascadia, and Barbados ridge subduction zones. We find that shallow subduction zone sediments in general have similarly low rigidity. These data provide important ground-truth values that can be used to parameterize fault slip models addressing the problem of shallow, tsunamigenic propagation of megathrust earthquakes.

Off-axis phonon and photon propagation in porous silicon superlattices studied by Brillouin spectroscopy and optical reflectance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsons, L. C., E-mail: lcparsons@mun.ca; Andrews, G. T., E-mail: tandrews@mun.ca

2014-07-21

Brillouin light scattering experiments and optical reflectance measurements were performed on a pair of porous silicon-based optical Bragg mirrors which had constituent layer porosity ratios close to unity. For off-axis propagation, the phononic and photonic band structures of the samples were modeled as a series of intersecting linear dispersion curves. Zone-folding was observed for the longitudinal bulk acoustic phonon and the frequency of the probed zone-folded longitudinal phonon was shown to be dependent on the propagation direction as well as the folding order of the mode branch. There was no conclusive evidence of coupling between the transverse and the foldedmore » longitudinal modes. Two additional observed Brillouin peaks were attributed to the Rayleigh surface mode and a possible pseudo-surface mode. Both of these modes were dispersive, with the velocity increasing as the wavevector decreased.« less

Velocity surface measurements for ZnO films over /001/-cut GaAs

NASA Technical Reports Server (NTRS)

Kim, Yoonkee; Hunt, William D.; Liu, Yongsheng; Jen, Cheng-Kuei

1994-01-01

A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

Mass-velocity and size-velocity distributions of ejecta cloud from shock-loaded tin surface using large scale molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Durand, Olivier; Soulard, Laurent

2015-06-01

The mass (volume and areal densities) versus velocity as well as the size versus velocity distributions of a shock-induced cloud of particles are investigated using large scale molecular dynamics (MD) simulations. A generic 3D tin crystal with a sinusoidal free surface roughness is set in contact with vacuum and shock-loaded so that it melts directly on shock. At the reflection of the shock wave onto the perturbations of the free surface, 2D sheets/jets of liquid metal are ejected. The simulations show that the distributions may be described by an analytical model based on the propagation of a fragmentation zone, from the tip of the sheets to the free surface, within which the kinetic energy of the atoms decreases as this zone comes closer to the free surface on late times. As this kinetic energy drives (i) the (self-similar) expansion of the zone once it has broken away from the sheet and (ii) the average size of the particles which result from fragmentation in the zone, the ejected mass and the average size of the particles progressively increase in the cloud as fragmentation occurs closer to the free surface. Though relative to nanometric scales, our model reproduces quantitatively experimental profiles and may help in their analysis.

Cohesive zone length of metagabbro at supershear rupture velocity

NASA Astrophysics Data System (ADS)

Fukuyama, Eiichi; Xu, Shiqing; Yamashita, Futoshi; Mizoguchi, Kazuo

2016-10-01

We investigated the shear strain field ahead of a supershear rupture. The strain array data along the sliding fault surfaces were obtained during the large-scale biaxial friction experiments at the National Research Institute for Earth Science and Disaster Resilience. These friction experiments were done using a pair of meter-scale metagabbro rock specimens whose simulated fault area was 1.5 m × 0.1 m. A 2.6-MPa normal stress was applied with loading velocity of 0.1 mm/s. Near-fault strain was measured by 32 two-component semiconductor strain gauges installed at an interval of 50 mm and 10 mm off the fault and recorded at an interval of 1 MHz. Many stick-slip events were observed in the experiments. We chose ten unilateral rupture events that propagated with supershear rupture velocity without preceding foreshocks. Focusing on the rupture front, stress concentration was observed and sharp stress drop occurred immediately inside the ruptured area. The temporal variation of strain array data is converted to the spatial variation of strain assuming a constant rupture velocity. We picked up the peak strain and zero-crossing strain locations to measure the cohesive zone length. By compiling the stick-slip event data, the cohesive zone length is about 50 mm although it scattered among the events. We could not see any systematic variation at the location but some dependence on the rupture velocity. The cohesive zone length decreases as the rupture velocity increases, especially larger than √{2} times the shear wave velocity. This feature is consistent with the theoretical prediction.

Diffusion Driven Combustion Waves in Porous Media

NASA Technical Reports Server (NTRS)

Aldushin, A. P.; Matkowsky, B. J.

2000-01-01

Filtration of gas containing oxidizer, to the reaction zone in a porous medium, due, e.g., to a buoyancy force or to an external pressure gradient, leads to the propagation of Filtration combustion (FC) waves. The exothermic reaction occurs between the fuel component of the solid matrix and the oxidizer. In this paper, we analyze the ability of a reaction wave to propagate in a porous medium without the aid of filtration. We find that one possible mechanism of propagation is that the wave is driven by diffusion of oxidizer from the environment. The solution of the combustion problem describing diffusion driven waves is similar to the solution of the Stefan problem describing the propagation of phase transition waves, in that the temperature on the interface between the burned and unburned regions is constant, the combustion wave is described by a similarity solution which is a function of the similarity variable x/square root of(t) and the wave velocity decays as 1/square root of(t). The difference between the two problems is that in the combustion problem the temperature is not prescribed, but rather, is determined as part of the solution. We will show that the length of samples in which such self-sustained combustion waves can occur, must exceed a critical value which strongly depends on the combustion temperature T(sub b). Smaller values of T(sub b) require longer sample lengths for diffusion driven combustion waves to exist. Because of their relatively small velocity, diffusion driven waves are considered to be relevant for the case of low heat losses, which occur for large diameter samples or in microgravity conditions, Another possible mechanism of porous medium combustion describes waves which propagate by consuming the oxidizer initially stored in the pores of the sample. This occurs for abnormally high pressure and gas density. In this case, uniformly propagating planar waves, which are kinetically controlled, can propagate, Diffusion of oxidizer decreases the wave velocity. In addition to the reaction and diffusion layers, the uniformly propagating wave structure includes a layer with a pressure gradient, where the gas motion is induced by the production or consumption of the gas in the reaction as well as by thermal expansion of the gas. The width of this zone determines the scale of the combustion wave in the porous medium.

Method for fabricating an ignitable heterogeneous stratified metal structure

DOEpatents

Barbee, T.W. Jr.; Weihs, T.

1996-08-20

A multilayer structure has a selectable: (1) propagating reaction front velocity V; (2) reaction initiation temperature attained by application of external energy; and (3) amount of energy delivered by a reaction of alternating unreacted layers of the multilayer structure. Because V is selectable and controllable, a variety of different applications for the multilayer structures are possible, including but not limited to their use as igniters, in joining applications, in fabrication of new materials, as smart materials and in medical applications and devices. The multilayer structure has a period D, and an energy release rate constant K. Two or more alternating unreacted layers are made of different materials and separated by reacted zones. The period D is equal to a sum of the widths of each single alternating reaction layer of a particular material, and also includes a sum of reacted zone widths, t{sub i}, in the period D. The multilayer structure has a selectable propagating reaction front velocity V, where V=K(1/D{sup n}){times}[1-(t{sub i}/D)] and n is about 0.8 to 1.2. 8 figs.

Method for fabricating an ignitable heterogeneous stratified metal structure

DOEpatents

Barbee, Jr., Troy W.; Weihs, Timothy

1996-01-01

A multilayer structure has a selectable, (i) propagating reaction front velocity V, (ii) reaction initiation temperature attained by application of external energy and (iii) amount of energy delivered by a reaction of alternating unreacted layers of the multilayer structure. Because V is selectable and controllable, a variety of different applications for the multilayer structures are possible, including but not limited to their use as ignitors, in joining applications, in fabrication of new materials, as smart materials and in medical applications and devices. The multilayer structure has a period D, and an energy release rate constant K. Two or more alternating unreacted layers are made of different materials and separated by reacted zones. The period D is equal to a sum of the widths of each single alternating reaction layer of a particular material, and also includes a sum of reacted zone widths, t.sub.i, in the period D. The multilayer structure has a selectable propagating reaction front velocity V, where V=K(1/D.sup.n).times.[1-(t.sub.i /D)]and n is about 0.8 to 1.2.

Investigating Complex Slow Slip Evolution with High-Resolution Tremor Catalogs and Numerical Simulations

NASA Astrophysics Data System (ADS)

Peng, Y.; Rubin, A. M.

2016-12-01

Significant complexities of episodic slip and tremor (ETS) have been revealed by short tremor bursts lasting minutes to hours, many of which show clear migration patterns. In Cascadia, large-scale rapid tremor reversals (RTRs) extend tens of km along strike, repeatedly occupying the same general source area during an ETS episode [e.g. Thomas et al, 2013; Peng and Rubin, 2016]. We also observe repetitive tremor bursts occurring well behind the main front in Guerrero, Mexico. In contrast to RTRs, these bursts do not originate from the main front, and generally propagate along the slip direction, similar to those reported from Shikoku, Japan [Shelly et al., 2007]. Both types of bursts occur intermittently, with recurrence intervals gradually increasing to tidal periods. However, even the tidally-modulated bursts are unlikely to be driven solely by tidal forcing. Since the stress must decrease during each burst, while the local maxima of the tidal stress remain nearly constant, each tidal peak stress cannot supply the stress drop for the next repetition. Here we explore the possibility that these repetitive bursts are driven by surrounding tremor-less slow slip. We develop a numerical model governed by a rate-and-state friction law that transitions from velocity-weakening to velocity-strengthening with increasing slip speed. A region with a larger transitional velocity than the background is used to represent the tremor zone. For this zone to slip intermittently, its stiffness needs to be sufficiently large that the slip during each burst is less than the total slip of the background during an episode, but smaller than its own critical stiffness. This critical stiffness decreases as the ratio of the background loading rate to the transitional cutoff velocity increases; from elasticity this ratio decreases as the main front moves across the model tremor zone. With these considerations, we successfully reproduce the burst-like behavior with increasingly large recurrence intervals in the model tremor zone during a single slow slip event. Future work will include investigating the propagation velocities of these bursts, which in Guerrero decrease systematically with increasing time since the previous migration through the same region, and tidal modulation of their recurrence intervals.

Nucleation and arrest of slow slip earthquakes: mechanisms and nonlinear simulations using realistic fault geometries and heterogeneous medium properties

NASA Astrophysics Data System (ADS)

Alves da Silva Junior, J.; Frank, W.; Campillo, M.; Juanes, R.

2017-12-01

Current models for slow slip earthquakes (SSE) assume a simplified fault embedded on a homogeneous half-space. In these models SSE events nucleate on the transition from velocity strengthening (VS) to velocity weakening (VW) down dip from the trench and propagate towards the base of the seismogenic zone, where high normal effective stress is assumed to arrest slip. Here, we investigate SSE nucleation and arrest using quasi-static finite element simulations, with rate and state friction, on a domain with heterogeneous properties and realistic fault geometry. We use the fault geometry of the Guerrero Gap in the Cocos subduction zone, where SSE events occurs every 4 years, as a proxy for subduction zone. Our model is calibrated using surface displacements from GPS observations. We apply boundary conditions according to the plate convergence rate and impose a depth-dependent pore pressure on the fault. Our simulations indicate that the fault geometry and elastic properties of the medium play a key role in the arrest of SSE events at the base of the seismogenic zone. SSE arrest occurs due to aseismic deformations of the domain that result in areas with elevated effective stress. SSE nucleation occurs in the transition from VS to VW and propagates as a crack-like expansion with increased nucleation length prior to dynamic instability. Our simulations encompassing multiple seismic cycles indicate SSE interval times between 1 and 10 years and, importantly, a systematic increase of rupture area prior to dynamic instability, followed by a hiatus in the SSE occurrence. We hypothesize that these SSE characteristics, if confirmed by GPS observations in different subduction zones, can add to the understanding of nucleation of large earthquakes in the seismogenic zone.

Pore Fluid Extraction by Reactive Solitary Waves in 3-D

NASA Astrophysics Data System (ADS)

Omlin, Samuel; Malvoisin, Benjamin; Podladchikov, Yury Y.

2017-09-01

In the lower crust, viscous compaction is known to produce solitary porosity and fluid pressure waves. Metamorphic (de)volatilization reactions can also induce porosity changes in response to the propagating fluid pressure anomalies. Here we present results from high-resolution simulations using Graphic Processing Unit parallel processing with a model that includes both viscous (de)compaction and reaction-induced porosity changes. Reactive porosity waves propagate in a manner similar to viscous porosity waves, but through a different mechanism involving fluid release and trap in the solid by reaction. These waves self-generate from red noise or an ellipsoidal porosity anomaly with the same characteristic size and abandon their source region to propagate at constant velocity. Two waves traveling at different velocities pass through each other in a soliton-like fashion. Reactive porosity waves thus provide an additional mechanism for fluid extraction at shallow depths with implications for ore formation, diagenesis, metamorphic veins formation, and fluid extraction from subduction zones.

The Architecture and Frictional Properties of Faults in Shale

NASA Astrophysics Data System (ADS)

De Paola, N.; Imber, J.; Murray, R.; Holdsworth, R.

2015-12-01

The geometry of brittle fault zones in shale rocks, as well as their frictional properties at reservoir conditions, are still poorly understood. Nevertheless, these factors may control the very low recovery factors (25% for gas and 5% for oil) obtained during fracking operations. Extensional brittle fault zones (maximum displacement < 3 m) cut exhumed oil mature black shales in the Cleveland Basin (UK). Fault cores up to 50 cm wide accommodated most of the displacement, and are defined by a stair-step geometry. Their internal architecture is characterised by four distinct fault rock domains: foliated gouges; breccias; hydraulic breccias; and a slip zone up to 20 mm thick, composed of a fine-grained black gouge. Hydraulic breccias are located within dilational jogs with aperture of up to 20 cm. Brittle fracturing and cataclastic flow are the dominant deformation mechanisms in the fault core of shale faults. Velocity-step and slide-hold-slide experiments at sub-seismic slip rates (microns/s) were performed in a rotary shear apparatus under dry, water and brine-saturated conditions, for displacements of up to 46 cm. Both the protolith shale and the slip zone black gouge display shear localization, velocity strengthening behaviour and negative healing rates, suggesting that slow, stable sliding faulting should occur within the protolith rocks and slip zone gouges. Experiments at seismic speed (1.3 m/s), performed on the same materials under dry conditions, show that after initial friction values of 0.5-0.55, friction decreases to steady-state values of 0.1-0.15 within the first 10 mm of slip. Contrastingly, water/brine saturated gouge mixtures, exhibit almost instantaneous attainment of very low steady-state sliding friction (0.1), suggesting that seismic ruptures may efficiently propagate in the slip zone of fluid-saturated shale faults. Stable sliding in faults in shale can cause slow fault/fracture propagation, affecting the rate at which new fracture areas are created and, hence, limiting oil and gas production during reservoir stimulation. However, fluid saturated conditions can favour seismic slip propagation, with fast and efficient creation of new fracture areas. These processes are very effective at dilational jogs, where fluid circulation may be enhanced, facilitating oil and gas production.

Study of internal gravity waves in the meteor zone

NASA Technical Reports Server (NTRS)

Gavrilov, N. M.

1987-01-01

An important component of the dynamical regime of the atmosphere at heights near 100 km are internal gravity waves (IGW) with periods from about 5 min to about 17.5 hrs which propagate from the lower atmospheric layers and are generated in the uppermost region of the atmosphere. As IGW propagate upwards, their amplitudes increase and they have a considerable effect on upper atmospheric processes: (1) they provide heat flux divergences comparable with solar heating; (2) they influence the gaseous composition and produce wave variations of the concentrations of gaseous components and emissions of the upper atmosphere; and (3) they cause considerable acceleration of the mean stream. It was concluded that the periods, wavelengths, amplitudes and velocities of IGW propagation in the meteor zone are now measured quite reliably. However, for estimating the influence of IGW on the thermal regime and the circulation of the upper atmosphere these parameters are not as important as the values of wave fluxes of energy, heat, moment and mass.

Development of lithotripter technology

NASA Astrophysics Data System (ADS)

Eisenmenger, Wolfgang F. W.

2003-10-01

``Squeezing'' of the stone or cirumferential pressure of the wave propagating at the outside of the stone in the liquid or tissue results in fragmentation in planes perpendicular or parallel to the wave propagation direction. The corresponding pressure zone propagating with the sound velocity in the liquid which is below the sound velocity in the stone, causes an evanescent pressure zone in the stone resulting in tensile stress in planes parallel and perpendicular to the wave plane. A quantitative model predicting the ratio of pulses needed to fragment the stone to 2 mm particle size in relation to the number of pressure pulses needed for the first fragmentation is well in accord with experiments, supporting the ``squeezing mechanism with binary fragmentation.'' On the basis of these results it now appears possible to optimize the pressure pulse parameters measured using the Fiber Optic Probe Hydrophone (FOPH). With correspondingly optimized self-focusing electromagnetic shock wave generator systems a clinical study of the concept ``wide focus and low pressure'' ESWL was performed in a scientific cooperation between the 1. Physical Institute of the University of Stuttgart and the Xixin Medical Instruments Co., Ltd. in Suzhou, China. Literature: W. Eisenmenger, ``The mechanisms of stone fragmentation in ESWL,'' Ultrasound Med. Biol. 27, 683-693 (2001); W. Eisenmenger et al., ``The first clinical results of `wide focus and low pressure' ESWL,'' Ultrasound Med. Biol. 28, 769-774 (2002).

Seismic Velocity and Elastic Properties of Plate Boundary Faults

NASA Astrophysics Data System (ADS)

Jeppson, Tamara N.

The elastic properties of fault zone rock at depth play a key role in rupture nucleation, propagation, and the magnitude of fault slip. Materials that lie within major plate boundary fault zones often have very different material properties than standard crustal rock values. In order to understand the mechanics of faulting at plate boundaries, we need to both measure these properties and understand how they govern the behavior of different types of faults. Mature fault zones tend to be identified in large-scale geophysical field studies as zones with low seismic velocity and/or electrical resistivity. These anomalous properties are related to two important mechanisms: (1) mechanical or diagenetic alteration of the rock materials and/or (2) pore fluid pressure and stress effects. However, in remotely-sensed and large-length-scale data it is difficult to determine which of these mechanisms are affecting the measured properties. The objective of this dissertation research is to characterize the seismic velocity and elastic properties of fault zone rocks at a range of scales, with a focus on understanding why the fault zone properties are different from those of the surrounding rock and the potential effects on earthquake rupture and fault slip. To do this I performed ultrasonic velocity experiments under elevated pressure conditions on drill core and outcrops samples from three plate boundary fault zones: the San Andreas Fault, California, USA; the Alpine Fault, South Island, New Zealand; and the Japan Trench megathrust, Japan. Additionally, I compared laboratory measurements to sonic log and large-scale seismic data to examine the scale-dependence of the measured properties. The results of this study provide the most comprehensive characterization of the seismic velocities and elastic properties of fault zone rocks currently available. My work shows that fault zone rocks at mature plate boundary faults tend to be significantly more compliant than surrounding crustal rocks and quantifies that relationship. The results of this study are particularly relevant to the interpretation of field-scale seismic datasets at major fault zones. Additionally, the results of this study provide constraints on elastic properties used in dynamic rupture models.

Validation of Born Traveltime Kernels

NASA Astrophysics Data System (ADS)

Baig, A. M.; Dahlen, F. A.; Hung, S.

2001-12-01

Most inversions for Earth structure using seismic traveltimes rely on linear ray theory to translate observed traveltime anomalies into seismic velocity anomalies distributed throughout the mantle. However, ray theory is not an appropriate tool to use when velocity anomalies have scale lengths less than the width of the Fresnel zone. In the presence of these structures, we need to turn to a scattering theory in order to adequately describe all of the features observed in the waveform. By coupling the Born approximation to ray theory, the first order dependence of heterogeneity on the cross-correlated traveltimes (described by the Fréchet derivative or, more colourfully, the banana-doughnut kernel) may be determined. To determine for what range of parameters these banana-doughnut kernels outperform linear ray theory, we generate several random media specified by their statistical properties, namely the RMS slowness perturbation and the scale length of the heterogeneity. Acoustic waves are numerically generated from a point source using a 3-D pseudo-spectral wave propagation code. These waves are then recorded at a variety of propagation distances from the source introducing a third parameter to the problem: the number of wavelengths traversed by the wave. When all of the heterogeneity has scale lengths larger than the width of the Fresnel zone, ray theory does as good a job at predicting the cross-correlated traveltime as the banana-doughnut kernels do. Below this limit, wavefront healing becomes a significant effect and ray theory ceases to be effective even though the kernels remain relatively accurate provided the heterogeneity is weak. The study of wave propagation in random media is of a more general interest and we will also show our measurements of the velocity shift and the variance of traveltime compare to various theoretical predictions in a given regime.

NOAA Propagation Database Value in Tsunami Forecast Guidance

NASA Astrophysics Data System (ADS)

Eble, M. C.; Wright, L. M.

2016-02-01

The National Oceanic and Atmospheric Administration (NOAA) Center for Tsunami Research (NCTR) has developed a tsunami forecasting capability that combines a graphical user interface with data ingestion and numerical models to produce estimates of tsunami wave arrival times, amplitudes, current or water flow rates, and flooding at specific coastal communities. The capability integrates several key components: deep-ocean observations of tsunamis in real-time, a basin-wide pre-computed propagation database of water level and flow velocities based on potential pre-defined seismic unit sources, an inversion or fitting algorithm to refine the tsunami source based on the observations during an event, and tsunami forecast models. As tsunami waves propagate across the ocean, observations from the deep ocean are automatically ingested into the application in real-time to better define the source of the tsunami itself. Since passage of tsunami waves over a deep ocean reporting site is not immediate, we explore the value of the NOAA propagation database in providing placeholder forecasts in advance of deep ocean observations. The propagation database consists of water elevations and flow velocities pre-computed for 50 x 100 [km] unit sources in a continuous series along all known ocean subduction zones. The 2011 Japan Tohoku tsunami is presented as the case study

Pulse-like partial ruptures and high-frequency radiation at creeping-locked transition during megathrust earthquakes

NASA Astrophysics Data System (ADS)

Michel, Sylvain; Avouac, Jean-Philippe; Lapusta, Nadia; Jiang, Junle

2017-08-01

Megathrust earthquakes tend to be confined to fault areas locked in the interseismic period and often rupture them only partially. For example, during the 2015 M7.8 Gorkha earthquake, Nepal, a slip pulse propagating along strike unzipped the bottom edge of the locked portion of the Main Himalayan Thrust (MHT). The lower edge of the rupture produced dominant high-frequency (>1 Hz) radiation of seismic waves. We show that similar partial ruptures occur spontaneously in a simple dynamic model of earthquake sequences. The fault is governed by standard laboratory-based rate-and-state friction with the aging law and contains one homogenous velocity-weakening (VW) region embedded in a velocity-strengthening (VS) area. Our simulations incorporate inertial wave-mediated effects during seismic ruptures (they are thus fully dynamic) and account for all phases of the seismic cycle in a self-consistent way. Earthquakes nucleate at the edge of the VW area and partial ruptures tend to stay confined within this zone of higher prestress, producing pulse-like ruptures that propagate along strike. The amplitude of the high-frequency sources is enhanced in the zone of higher, heterogeneous stress at the edge of the VW area.

Pulse-Like Partial Ruptures and High-Frequency Radiation at Creeping-Locked Transition during Megathrust Earthquakes

NASA Astrophysics Data System (ADS)

Michel, S. G. R. M.; Avouac, J. P.; Lapusta, N.; Jiang, J.

2017-12-01

Megathrust earthquakes tend to be confined to fault areas locked in the interseismic period and often rupture them only partially. For example, during the 2015 M7.8 Gorkha earthquake, Nepal, a slip pulse propagating along strike unzipped the bottom edge of the locked portion of the Main Himalayan Thrust (MHT). The lower edge of the rupture produced dominant high-frequency (>1 Hz) radiation of seismic waves. We show that similar partial ruptures occur spontaneously in a simple dynamic model of earthquake sequences. The fault is governed by standard laboratory-based rate-and-state friction with the ageing law and contains one homogenous velocity-weakening (VW) region embedded in a velocity-strengthening (VS) area. Our simulations incorporate inertial wave-mediated effects during seismic ruptures (they are thus fully dynamic) and account for all phases of the seismic cycle in a self-consistent way. Earthquakes nucleate at the edge of the VW area and partial ruptures tend to stay confined within this zone of higher prestress, producing pulse-like ruptures that propagate along strike. The amplitude of the high-frequency sources is enhanced in the zone of higher, heterogeneous stress at the edge of the VW area.

Prediction of fingering in porous media

NASA Astrophysics Data System (ADS)

Wang, Zhi; Feyen, Jan; Elrick, David E.

1998-09-01

Immiscible displacement, involving two fluids in a porous medium, can be unstable and fingered under certain conditions. In this paper, the original linear instability criterion of Chuoke et al. [1959] is generalized, considering wettability of two immiscible fluids to the porous medium. This is then used to predict 24 specific flow and porous medium conditions for the onset of wetting front instability in the subsurface. Wetting front instability is shown to be a function of the driving fluid wettability to the medium, differences in density and viscosity of the fluids, the magnitude of the interfacial tension, and the direction of flow with respect to gravity. Scenarios of water and nonaqueous-phase liquid infiltration into the vadose zone are examined to predict preferential flow and contamination of groundwater. The mechanisms of finger formation, propagation, and persistence in the vadose zone are reviewed, and the existing equations for calculating the size, the number and velocity of fingers are simplified for field applications. The analyses indicate that fingers initiate and propagate according to spatial and temporal distribution of the dynamic breakthrough (water- or air-entry) pressures in the porous medium. The predicted finger size and velocity are in close agreement with the experimental results.

Seismic fault zone trapped noise

NASA Astrophysics Data System (ADS)

Hillers, G.; Campillo, M.; Ben-Zion, Y.; Roux, P.

2014-07-01

Systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics. Here we construct trapped waves from the scattered seismic wavefield recorded by a fault zone array. The frequency-dependent interaction between the ambient wavefield and the fault zone environment is studied using properties of the noise correlation field. A critical frequency fc ≈ 0.5 Hz defines a threshold above which the in-fault scattered wavefield has increased isotropy and coherency compared to the ambient noise. The increased randomization of in-fault propagation directions produces a wavefield that is trapped in a waveguide/cavity-like structure associated with the low-velocity damage zone. Dense spatial sampling allows the resolution of a near-field focal spot, which emerges from the superposition of a collapsing, time reversed wavefront. The shape of the focal spot depends on local medium properties, and a focal spot-based fault normal distribution of wave speeds indicates a ˜50% velocity reduction consistent with estimates from a far-field travel time inversion. The arrival time pattern of a synthetic correlation field can be tuned to match properties of an observed pattern, providing a noise-based imaging tool that can complement analyses of trapped ballistic waves. The results can have wide applicability for investigating the internal properties of fault damage zones, because mechanisms controlling the emergence of trapped noise have less limitations compared to trapped ballistic waves.

Density and Ultrasonic Characterization of Oil Palm Trunk Infected by Ganoderma Boninense Disease

NASA Astrophysics Data System (ADS)

Najmie, M. M. K.; Khalid, K.; Sidek, A. A.; Jusoh, M. A.

2011-01-01

Oil palm trunks infected by Ganoderma boninense disease have been studied using density and ultrasonic characterizations. The ultrasonic characterizations have been performed using a commercial ultrasonic instrument at the frequency of 54 kHz. The measurements have been done in 3 zones: inner zone, central zone and peripheral zone. It was found that the stem density of the oil palm infected by Ganoderma boninense disease was reduced by 50% in comparison to the original healthy trunk. From this effect the velocity of the ultrasonic wave propagated through the Longitudinal, Radial, and Tangential directions is lower for the trunk infected by Ganoderma boninense disease compared to a healthy trunk. For the 10 cm thickness of samples, the ultrasonic velocity for all transit directions was in range of 260 - 750 ms-1 for the infected sample, whereas for healthy samples was in the range of 460 - 900 ms-1. These results are very useful for the detection of the area which has been affected by the disease.

Estimation of seismic velocity changes at different depths associated with the 2014 Northern Nagano Prefecture earthquake, Japan ( M W 6.2) by joint interferometric analysis of NIED Hi-net and KiK-net records

NASA Astrophysics Data System (ADS)

Sawazaki, Kaoru; Saito, Tatsuhiko; Ueno, Tomotake; Shiomi, Katsuhiko

2016-12-01

To estimate the seismic velocity changes at different depths associated with a large earthquake, we apply passive image interferometry to two types of seismograms: KiK-net vertical pairs of earthquake records and Hi-net continuous borehole data. We compute the surface/borehole deconvolution waveform (DCW) of seismograms recorded by a KiK-net station and the autocorrelation function (ACF) of ambient noise recorded by a collocated Hi-net station, 26 km from the epicenter of the 2014 Northern Nagano Prefecture earthquake, Japan ( M W 6.2). Because the deeper KiK-net sensor and the Hi-net sensor are collocated at 150 m depth, and another KiK-net sensor is located at the surface directly above the borehole sensors, we can measure shallow (<150 m depth) and deep (>150 m depth) velocity changes separately. The sensitivity of the ACF to the velocity changes in the deeper zone is evaluated by a numerical wave propagation simulation. We detect relative velocity changes of -3.1 and -1.4% in the shallow and deep zones, respectively, within 1 week of the mainshock. The relative velocity changes recover to -1.9 and -1.1%, respectively, during the period between 1 week and 4 months after the mainshock. The observed relative velocity reductions can be attributed to dynamic strain changes due to the strong ground motion, rather than static strain changes due to coseismic deformation by the mainshock. The speed of velocity recovery may be faster in the shallow zone than in the deep zone because the recovery speed is controlled by initial damage in the medium. This recovery feature is analogous to the behavior of slow dynamics observed in rock experiments.

Optimal parameters of leader development in lightning

NASA Technical Reports Server (NTRS)

Petrov, N. I.; Petrova, G. N.

1991-01-01

The dependences between the different parameters of a leader in lightning are obtained theoretically. The physical mechanism of the instability leading to the formation of the streamer zone is proposed. The instability has the wave nature and is caused by the self-influence effects of the space charge. Using a stability condition of the leader propagation, a dependence is obtained between the current across the leader head and its velocity of motion. The dependence of the streamer zone length on the gap length is also obtained. It is shown that the streamer zone length is saturated with the increasing of the gap length. A comparison between the obtained dependences and the experimental data is presented.

Study on Water Distribution Imaging in the Sand Using Propagation Velocity of Sound with Scanning Laser Doppler Vibrometer

NASA Astrophysics Data System (ADS)

Sugimoto, Tsuneyoshi; Nakagawa, Yutaka; Shirakawa, Takashi; Sano, Motoaki; Ohaba, Motoyoshi; Shibusawa, Sakae

2013-07-01

We propose a method for the monitoring and imaging of the water distribution in the rooting zone of plants using sound vibration. In this study, the water distribution measurement in the horizontal and vertical directions in the soil layer was examined to confirm whether a temporal change in the volume water content of the soil could be estimated from a temporal changes in propagation velocity. A scanning laser Doppler vibrometer (SLDV) is used for measurement of the vibration velocity of the soil surface, because the highly precise vibration velocity measurement of several many points can be carried out automatically. Sand with a uniform particle size distribution is used for the soil, as it has high plasticity; that is, the sand can return to a dry state easily even if it is soaked with water. A giant magnetostriction vibrator or a flat speaker is used as a sound source. Also, a soil moisture sensor, which measures the water content of the soil using the electric permittivity, is installed in the sand. From the experimental results of the vibration measurement and soil moisture sensors, we can confirm that the temporal changes of the water distribution in sand using the negative pressure irrigation system in both the horizontal and vertical directions can be estimated using the propagation velocity of sound. Therefore, in the future, we plan to develop an insertion-type sound source and receiver using the acceleration sensors, and we intend to examine whether our method can be applied even in commercial soil with growing plants.

Shock Wave Propagation in Layered Planetary Interiors: Revisited

NASA Astrophysics Data System (ADS)

Arkani-Hamed, J.; Monteux, J.

2017-12-01

The end of the terrestrial planet accretion is characterized by numerous large impacts. About 90% of the mass of a large planet is accreted while the core mantle separation is occurring, because of the accretionary and the short-lived radio-isotope heating. The characteristics of the shockwave propagation, hence the existing scaling laws are poorly known within the layered planets. Here, we use iSALE-2D hydrocode simulations to calculate shock pressure in a differentiated Mars type body for impact velocities of 5-20 km/s, and impactor sizes of 100-400 km. We use two different rheologies for the target interior, an inviscid model ("no-stress model") and a pressure and damage-dependent strength model ("elaborated model"). To better characterize the shock pressure within the whole mantle as a function of distance from the impact site, we propose the following distribution: (1) a near field zone larger than the isobaric core that extends to 7-15 times the projectile radius into the target, where the peak shock pressure decays exponentially with increasing distance, (2) a far field zone where the pressure decays with distance following a power law. The shock pressure decreases more rapidly with distance in the near field for the elaborated model than for the no-stress model because of the influence of acoustic fluidization and damage. However to better illustrate the influence of the rheology on the shock propagation, we use the same expressions to fit the shock pressure with distance for both models. At the core-mantle boundary, CMB, the peak shock pressure jumps as the shock wave enters the core. We derived the boundary condition at CMB for the peak shock pressure. It is less sensitive to the impact velocity or the impactor size, but strongly depends on the rheology of the planet's mantle. Because of the lower shock wave velocity in the core compared to that in the mantle, the refracted shockwave propagates toward the symmetry axis of the planet, and the shock pressure in the core decreases following a second power law. In this study, we express the output obtained from iSALE hydrocodes by scaling laws to illustrate the influence of the ray angle relative to the axis of symmetry, the target rheology, the impactor size and the impact velocity. We use these shock-pressure scaling laws to determine the impact heating of terrestrial planets.

Strain Partitioning and Accumulation across Overlapping Spreading Centers: Geodetic GPS Measurements in South Iceland

NASA Astrophysics Data System (ADS)

La Femina, P. C.; Dixon, T. H.; Malservisi, R.; Árnadóttir, T.; Sigmundsson, F.; Sturkell, E.

2004-12-01

Overlapping spreading centers (OSCs) and propagating ridges are important classes of mid-ocean ridges. Kinematic models of OSCs predict along strike variability in spreading rate associated with the propagation of one center and deactivation of the other. Iceland offers a unique opportunity to investigate strain accumulation and partitioning across slow, overlapping spreading centers, and the influence of a ridge centered hotspot on ridge kinematics and morphology. We present results of detailed GPS observations across the Eastern and Western Volcanic Zones, south Iceland, spanning a seven to nine year inter-rifting period, and compare our observations with two-dimensional elastic half-space models that simulate the long-term spreading process. We then compare the elastic half-space models with simple viscoelastic coupling models. We model three velocity profiles across the EVZ-WVZ system, solving for the spreading rate, locking depth and horizontal location of each spreading center. Our spreading rate estimates indicate along strike variations as expected in an OSC system and total spreading rates consistent with geodetic and geologic plate motion models. Spreading rates in the WVZ increase from northeast (3 ±1 mm/yr) to southwest (7 ±1 mm/yr). Spreading rates in the southwest propagating EVZ decrease from northeast (17 ±1 mm/yr) to southwest (12 ±1 mm/yr). These results are consistent with a model whereby the WVZ is deactivating in the direction of EVZ propagation. The morphology of the two spreading centers reflects the spreading rate differences and their location relative to the Iceland hotspot. The predicted locations of the spreading axis for each zone are consistent with mapped Holocene fissure swarms. The neovolcanic zone of the slower WVZ consists of a narrow (10-20 km wide) axial graben and has had few Holocene eruptions. The faster EVZ consists of two parallel neovolcanic zones separated by a 20 km gap of inactivity, little normal faulting, higher topography and five historical fissure eruptions, reflecting its proximity to the hotspot. The maximum velocity gradient in the EVZ is located on the Veidivotn fissure swarm, which had a small volume eruption in 1864. The last major fissure eruption in the EVZ was the 1783 Lakagigar, located 20 km to the east. This pattern of current and past strain accumulation and release suggests intra-ridge jumping of activity and crustal accretion across a 60 km wide area.

On the integral manifold approach to a flame propagation problem

NASA Astrophysics Data System (ADS)

Bykov, Viatcheslav; Goldfarb, Igor; Gol'Dshtein, Vladimir

2004-08-01

The problem of a pressure-driven flame in an inert porous medium filled with a flammable gaseous mixture is considered. In the frame of reference attached to an advancing combustion wave and after a suitable non-dimensionalization the corresponding mathematical description of the problem includes three highly nonlinear ordinary differential equations. The system is rewritten in the form of a singularly perturbed system of ordinary differential equations and is analysed analytically by the geometrical version of the asymptotic method of integral manifolds (MIM). The paper focuses on an analysis of the fine structure of the flame and its velocity on the basis of an asymptotical consideration of an arbitrary trajectory of the considered system in the phase space. It is shown that two different stages of the trajectory correspond to the two various sub-zones of the flame: the first stage (fast motion from the initial point to the slow integral) is interpreted as a preheat sub-zone and the second stage of the path corresponds to a reaction sub-zone. It is shown that an inter-zone boundary plays an important role in a determination of the flame properties: characteristics of the gaseous mixture at that point determine the flame velocity. The accepted approach of the investigation allows us to gain an analytical expression for the flame velocity. It appears that the velocity formula represents a cubic-root dependence on the Arrhenius exponent, which in turn contains the parameters of the boundary point. The theoretical predictions are found to coincide rather well with the data of direct numerical simulations.

Rift Zone Abandonment and Reconfiguration in Hawaii: Evidence from Mauna Loa’s Ninole Rift Zone

NASA Astrophysics Data System (ADS)

Morgan, J. K.; Park, J.; Zelt, C. A.

2009-12-01

Large oceanic volcanoes commonly develop elongate rift zones that disperse viscous magmas to the distal reaches of the edifice. Intrusion and dike propagation occur under tension perpendicular to the rift zone, controlled by topography, magmatic pressures, and deformation of the edifice. However, as volcanoes grow and interact, the controlling stress fields can change, potentially altering the orientations and activities of rift zones. This phenomenon is probably common, and can produce complex internal structures that influence the evolution of a volcano and its neighbors. However, little direct evidence for such rift zone reconfiguration exists, primarily due to poor preservation or recognition of earlier volcanic configurations. A new onshore-offshore 3-D seismic velocity model for the Island of Hawaii, derived from a joint tomographic inversion of an offshore airgun shot - onshore receiver geometry and earthquake sources beneath the island, demonstrates a complicated history of rift zone reconfiguration on Mauna Loa volcano, Hawaii, including wholesale rift zone abandonment. Mauna Loa’s southeast flank contains a massive high velocity intrusive complex, now buried beneath flows derived from Mauna Loa’s active southwest rift zone (SWRZ). Introduced here as the Ninole Rift Zone, this feature extends more than 60 km south of Mauna Loa’s summit, spans a depth range of ~2-14 km below sea level, and is the probable source of the 100-200 ka Ninole volcanics in several prominent erosional hills. A lack of high velocities beneath the upper SWRZ and its separate zone of high velocities on the submarine flank, indicate that the younger rift zone was built upon a pre-existing edifice that emanated from the Ninole rift zone. The ancient Ninole rift zone may stabilize Mauna Loa’s southeast flank, focusing recent volcanic activity and deformation onto the unbuttressed west flank. The upper portion of the Ninole rift zone appears to have migrated westward over time, possibly triggered by landsliding, causing its eventual abandonment in preference to Mauna Loa’s present-day SWRZ. Subsequently, the lower SWRZ broke away, tracking rift intrusions along the trace of the Kahuku detachment fault. Similar rift zone migration is thought to be underway at Kilauea volcano, and may one-day lead to the abandonment of the east rift zone. Such rift zone reconfiguration is a reflection of changing stress conditions within growing volcanoes. It is probably much more common than previously assumed, and may enable the growth of very large volcanic edifices such as Mauna Loa.

Study of the surface wave off-great-circle propagation based on dense seismic array: a case study in Northeast China

NASA Astrophysics Data System (ADS)

Chen, H.; Chong, J.

2016-12-01

The traditional surface wave tomography is based on the ray theory, which assumes that surface wave propagates along the great-circle. The great-circle assumption is valid only when the size of the anomaly is larger than the width of the Fresnel zone and the lateral variation is relatively smooth. However, off-great-circle propagation may occur when the surface wave travels across tectonic boundaries with strong heterogeneity and sharp velocity change, e.g., continental margin, mid-ridge and sea trench, resulting in arrival angle anomaly and multi-pathing effect. The off-great-circle propagation may deviate the result of surface wave tomography based on great-circle approximation, so it is of great importance to study the off-great-circle propagation. In this study, we used the teleseismic waveforms from September 2009 to August 2011, recorded by the NECESSArray in Northeast China, to study the off-great-circle propagation of Rayleigh wave by the Beamforming method. Our results show that the off-great-circle effect increases with decreasing period. At the period of 60 s, the off-great-circle effect is relatively weak and the Rayleigh wave propagates approximately along the great-circle. While at the period of 20 s, the off-great-circle effect becomes strong, the arrival angle anomaly measured from some events can be as large as 20º, and obvious multi-pathing effect is also observed. Lateral variations of the arrival angle anomaly and phase velocity have also been found in the study region, which may be correlated with the lithosphere heterogeneity in Northeast China. Our results demonstrate the necessity to study the surface wave off-great-circle propagation. Acknowledgement: This study is financially supported by National Natural Science Foundation of China under Grant No. 41590854.

Geophysical evidence for a transform margin in Northwestern Algeria: possible vestige of a Subduction-Transform Edge Propagator

NASA Astrophysics Data System (ADS)

Badji, R.; Charvis, P.; Bracene, R.; Galve, A.; Badsi, M.; Ribodetti, A.; Benaissa, Z.; Klingelhoefer, F.; Medaouri, M.; Beslier, M.

2013-12-01

This work is part of the Algerian-French SPIRAL program (Sismique Profonde et Investigation Régionale du Nord de l'Algérie) which provides unprecedented images of the deep structure of the western Algerian Margin based on several wide-angle and multichannel seismic data shot across the Algerian Margin. One of the different hypotheses for the opening of the western Mediterranean Sea, we are testing is that the western part of the Algerian margin was possibly part of the southern edge of the Alboran continental block during its westward migration related to the rollback of the Betic-Rif-Alboran subduction zone. A tomographic inversion of the first arrival traveltimes along a 100-km long wide-angle seismic profile shot over 40 Ocean Bottom Seismometers, across the Margin offshore Mostaganem (Northwestern Algerian Margin) was conducted. The final model reveals striking feature in the deep structure of the margin from north to south: 1- the oceanic crust is as thin as 4-km, with velocities ranging from 5.0 to 7.1 km/s, covered by a 3.3 km thick sedimentary pile (seismic velocities from 1.5 to 5.0 km/s) characterized by an intense diapiric activity of the Messinian salt layer. 2- a sharp transition zone, less than 10 km wide, with seismic velocities intermediate between oceanic seismic velocities (observed northward) and continental seismic velocities (observed southward). This zone coincides with narrow and elongated pull apart basins imaged by multichannel seismic data. No evidence of volcanism nor of exhumed serpentinized upper mantle as described along many extensional continental margins are observed along this segment of the margin. 3- a thinned continental crust coincident with a rapid variation of the Moho depth imaged from 12 to ~20 km with a dip up to 50%. The seafloor bathymetry is showing a steep continental slope (>20%). Either normal or inverse faults are observed along MCS lines shot in the dip direction but they do not present large vertical displacement and could be related primarily to strike slip motion. These results support the hypothesis, that the margin offshore Mostaganem is not an extensional margin but rather a transform margin. There is little evidence of tectonic inversion as described eastward along the Kabylian Margin. Possibly strike slip motion affected the thinned continental crust and the transition zone suggesting that this margin is a vestige of the Subduction-Transform Edge Propagator (STEP) related to the westward migration of the Alboran block.

Rupture dynamics along bimaterial interfaces: a parametric study of the coupling between interfacial sliding and normal traction perturbation

NASA Astrophysics Data System (ADS)

Scala, Antonio; Festa, Gaetano; Vilotte, Jean-Pierre

2017-04-01

Earthquake ruptures often develop along faults separating materials with dissimilar elastic properties. Due to the broken symmetry, the propagation of the rupture along the bimaterial interface is driven by the coupling between interfacial sliding and normal traction perturbations. We numerically investigate in-plane rupture growth along a planar interface, under slip weakening friction, separating two dissimilar isotropic linearly elastic half-spaces. We perform a parametric study of the classical Prakash-Clifton regularisation for different material contrasts. In particular mesh-dependence and regularisation-dependence of the numerical solutions are analysed in this parameter space. When regularisation involves a slip-rate dependent relaxation time, a characteristic sliding distance is identified below which numerical solutions no longer depend on the regularisation parameter, i.e. they are consistent solutions of the same physical problem. Such regularisation provides an adaptive high-frequency filter of the slip-induced normal traction perturbations, following the dynamic shrinking of the dissipation zone during the acceleration phase. In contrast, regularisation involving a constant relaxation time leads to numerical solutions that always depend on the regularisation parameter since it fails adapting to the shrinking of the process zone. Dynamic regularisation is further investigated using a non-local regularisation based on a relaxation time that depends on the dynamic length of the dissipation zone. Such reformulation is shown to provide similar results as the dynamic time scale regularisation proposed by Prakash-Clifton when slip rate is replaced by the maximum slip rate along the sliding interface. This leads to the identification of a dissipative length scale associated with the coupling between interfacial sliding and normal traction perturbations, together with a scaling law between the maximum slip rate and the dynamic size of the process zone during the rupture propagation. Dynamic time scale regularisation is show to provide mesh-independent and physically well-posed numerical solutions during the acceleration phase toward an asymptotic speed. When generalised Rayleigh wave does not exist, numerical solutions are shown to tend toward an asymptotic velocity higher than the slowest shear wave speed. When generalised Rayleigh wave speed exists, as numerical solutions tend toward this velocity, increasing spurious oscillations develop and solutions become unstable. In this regime regularisation dependent and unstable finite-size pulses may be generated. This instability is associated with the singular behaviour of the slip-induced normal traction perturbations, and of the slip rate at the rupture front, in relation with complete shrinking of the dissipation zone. This phase requires to be modelled either by more complex interface constitutive laws involving velocity-strengthening effects that may stabilize short wavelength interfacial propagating modes or by considering non-ideal interfaces that introduce a new length scale in the problem that may promote selection and stabilization of the slip pulses.

Multi-Scale Structure and Earthquake Properties in the San Jacinto Fault Zone Area

NASA Astrophysics Data System (ADS)

Ben-Zion, Y.

2014-12-01

I review multi-scale multi-signal seismological results on structure and earthquake properties within and around the San Jacinto Fault Zone (SJFZ) in southern California. The results are based on data of the southern California and ANZA networks covering scales from a few km to over 100 km, additional near-fault seismometers and linear arrays with instrument spacing 25-50 m that cross the SJFZ at several locations, and a dense rectangular array with >1100 vertical-component nodes separated by 10-30 m centered on the fault. The structural studies utilize earthquake data to image the seismogenic sections and ambient noise to image the shallower structures. The earthquake studies use waveform inversions and additional time domain and spectral methods. We observe pronounced damage regions with low seismic velocities and anomalous Vp/Vs ratios around the fault, and clear velocity contrasts across various sections. The damage zones and velocity contrasts produce fault zone trapped and head waves at various locations, along with time delays, anisotropy and other signals. The damage zones follow a flower-shape with depth; in places with velocity contrast they are offset to the stiffer side at depth as expected for bimaterial ruptures with persistent propagation direction. Analysis of PGV and PGA indicates clear persistent directivity at given fault sections and overall motion amplification within several km around the fault. Clear temporal changes of velocities, probably involving primarily the shallow material, are observed in response to seasonal, earthquake and other loadings. Full source tensor properties of M>4 earthquakes in the complex trifurcation area include statistically-robust small isotropic component, likely reflecting dynamic generation of rock damage in the source volumes. The dense fault zone instruments record seismic "noise" at frequencies >200 Hz that can be used for imaging and monitoring the shallow material with high space and time details, and numerous minute local earthquakes that contribute to the high frequency "noise". Updated results will be presented in the meeting. *The studies have been done in collaboration with Frank Vernon, Amir Allam, Dimitri Zigone, Zach Ross, Gregor Hillers, Ittai Kurzon, Michel Campillo, Philippe Roux, Lupei Zhu, Dan Hollis, Mitchell Barklage and others.

In situ observation of self-propagating high temperature syntheses of Ta5Si3, Ti5Si3 and TiB2 by proton and X-ray radiography

NASA Astrophysics Data System (ADS)

Bernert, T.; Winkler, B.; Haussühl, E.; Trouw, F.; Vogel, S. C.; Hurd, A. J.; Smilowitz, L.; Henson, B. F.; Merrill, F. E.; Morris, C. L.; Mariam, F. G.; Saunders, A.; Juarez-Arellano, E. A.

2013-08-01

Self-propagating high temperature reactions of tantalum and titanium with silicon and titanium with boron were studied using proton and X-ray radiography, small-angle neutron scattering, neutron time-of-flight, X-ray and neutron diffraction, dilatometry and video recording. We show that radiography allows the observation of the propagation of the flame front in all investigated systems and the determination of the widths of the burning zones. X-ray and neutron diffraction showed that the reaction products consisted of ≈90 wt% of the main phase and one or two secondary phases. For the reaction 5Ti + 3Si → Ti5Si3 flame front velocities of 7.1(3)-34.2(4) mm/s were determined depending on the concentration of a retardant added to the starting material, the geometry and the green density of the samples. The flame front width was determined to be 1.17(4)-1.82(8) mm and depends exponentially on the flame front velocity. Similarly, for the reaction Ti + 2B → TiB2 flame front velocities of 15(2)-26.6(4) mm/s were determined, while for a 5Ta + 3Si → Ta5Si3 reaction the flame front velocity was 7.05(4) mm/s. The micro structure of the product phase Ta5Si3 shows no texture. From SANS measurements the dependence of the specific surface of the product phase on the particle sizes of the starting materials was studied.

Instrument Correction and Dynamic Site Profile Validation at the Central United States Seismic Observatory, New Madrid Seismic Zone

NASA Astrophysics Data System (ADS)

Brengman, C.; Woolery, E. W.; Wang, Z.; Carpenter, S.

2016-12-01

The Central United States Seismic Observatory (CUSSO) is a vertical seismic array located in southwestern Kentucky within the New Madrid seismic zone. It is intended to describe the effects of local geology, including thick sediment overburden, on seismic-wave propagation, particularly strong-motion. The three-borehole array at CUSSO is composed of seismic sensors placed on the surface, and in the bedrock at various depths within the 585 m thick sediment overburden. The array's deep borehole provided a unique opportunity in the northern Mississippi embayment for the direct geological description and geophysical measurement of the complete late Cretaceous-Quaternary sediment column. A seven layer, intra-sediment velocity model is interpreted from the complex, inhomogeneous stratigraphy. The S- and P-wave sediment velocities range between 160 and 875 m/s and between 1000 and 2300 m/s, respectively, with bedrock velocities of 1452 and 3775 m/s, respectively. Cross-correlation and direct comparisons were used to filter out the instrument response and determine the instrument orientation, making CUSSO data ready for analysis, and making CUSSO a viable calibration site for other free-field sensors in the area. The corrected bedrock motions were numerically propagated through the CUSSO soil profile (transfer function) and compared, in terms of both peak acceleration and amplitude spectra, to the recorded surface observations. Initial observations reveal a complex spectral mix of amplification and de-amplification across the array, indicating the site effect in this deep sediment setting is not simply generated by the shallowest layers.

Fault Wear by Damage Evolution During Steady-State Slip

NASA Astrophysics Data System (ADS)

Lyakhovsky, Vladimir; Sagy, Amir; Boneh, Yuval; Reches, Ze'ev

2014-11-01

Slip along faults generates wear products such as gouge layers and cataclasite zones that range in thickness from sub-millimeter to tens of meters. The properties of these zones apparently control fault strength and slip stability. Here we present a new model of wear in a three-body configuration that utilizes the damage rheology approach and considers the process as a microfracturing or damage front propagating from the gouge zone into the solid rock. The derivations for steady-state conditions lead to a scaling relation for the damage front velocity considered as the wear-rate. The model predicts that the wear-rate is a function of the shear-stress and may vanish when the shear-stress drops below the microfracturing strength of the fault host rock. The simulated results successfully fit the measured friction and wear during shear experiments along faults made of carbonate and tonalite. The model is also valid for relatively large confining pressures, small damage-induced change of the bulk modulus and significant degradation of the shear modulus, which are assumed for seismogenic zones of earthquake faults. The presented formulation indicates that wear dynamics in brittle materials in general and in natural faults in particular can be understood by the concept of a "propagating damage front" and the evolution of a third-body layer.

A fault constitutive relation accounting for thermal pressurization of pore fluid

USGS Publications Warehouse

Andrews, D.J.

2002-01-01

The heat generated in a slip zone during an earthquake can raise fluid pressure and thereby reduce frictional resistance to slip. The amount of fluid pressure rise depends on the associated fluid flow. The heat generated at a given time produces fluid pressure that decreases inversely with the square root of hydraulic diffusivity times the elapsed time. If the slip velocity function is crack-like, there is a prompt fluid pressure rise at the onset of slip, followed by a slower increase. The stress drop associated with the prompt fluid pressure rise increases with rupture propagation distance. The threshold propagation distance at which thermally induced stress drop starts to dominate over frictionally induced stress drop is proportional to hydraulic diffusivity. If hydraulic diffusivity is 0.02 m2/s, estimated from borehole samples of fault zone material, the threshold propagation distance is 300 m. The stress wave in an earthquake will induce an unknown amount of dilatancy and will increase hydraulic diffusivity, both of which will lessen the fluid pressure effect. Nevertheless, if hydraulic diffusivity is no more than two orders of magnitude larger than the laboratory value, then stress drop is complete in large earthquakes.

Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays

NASA Astrophysics Data System (ADS)

Qin, L.; Ben-Zion, Y.; Qiu, H.; Share, P.-E.; Ross, Z. E.; Vernon, F. L.

2018-04-01

We image the internal structure of the San Jacinto fault zone (SJFZ) in the trifurcation area southeast of Anza, California, with seismic records from dense linear and rectangular arrays. The examined data include recordings from more than 20 000 local earthquakes and nine teleseismic events. Automatic detection algorithms and visual inspection are used to identify P and S body waves, along with P- and S-types fault zone trapped waves (FZTW). The location at depth of the main branch of the SJFZ, the Clark fault, is identified from systematic waveform changes across lines of sensors within the dense rectangular array. Delay times of P arrivals from teleseismic and local events indicate damage asymmetry across the fault, with higher damage to the NE, producing a local reversal of the velocity contrast in the shallow crust with respect to the large-scale structure. A portion of the damage zone between the main fault and a second mapped surface trace to the NE generates P- and S-types FZTW. Inversions of high-quality S-type FZTW indicate that the most likely parameters of the trapping structure are width of ˜70 m, S-wave velocity reduction of 60 per cent, Q value of 60 and depth of ˜2 km. The local reversal of the shallow velocity contrast across the fault with respect to large-scale structure is consistent with preferred propagation of earthquake ruptures in the area to the NW.

Dual-dye optical mapping after myocardial infarction: does the site of ventricular stimulation alter the properties of electrical propagation?

PubMed

Saba, Samir; Mathier, Michael A; Mehdi, Haider; Liu, Tong; Choi, Bum-Rak; London, Barry; Salama, Guy

2008-02-01

Myocardial infarction (MI) disrupts electrical conduction in affected ventricular areas. We investigated the effect of MI on the regional voltage and calcium (Ca) signals and their propagation properties, with special attention to the effect of the site of ventricular pacing on these properties. New Zealand White rabbits were divided into four study groups: sham-operated (C, n = 6), MI with no pacing (MI, n = 7), MI with right ventricular pacing (MI + RV, n = 6), and MI with BIV pacing (MI + BIV, n = 7). At 4 weeks, hearts were excised, perfused, and optically mapped. As previously shown, systolic and diastolic dilation of the LV were prevented by BIV pacing, as was the reduction in LV fractional shortening. Four weeks after MI, optical mapping revealed markedly reduced action potential amplitudes and conduction velocities (CV) in MI zones, and these increased gradually in the border zone and normal myocardial areas. Also, Ca transients were absent in the infarcted areas and increased gradually 3-5 mm from the border of the normal zone. Neither BIV nor RV pacing affected these findings in any of the MI, border, or normal zones. MI has profound effects on the regional electrical and Ca signals and on their propagation properties in this rabbit model. The absence of differences in these parameters by study group suggests that altering the properties of myocardial electrical conduction and Ca signaling are unlikely mechanisms by which BIV pacing confers its benefits. Further studies into the regional, cellular, and molecular benefits of BIV pacing are therefore warranted.

The effect of mineral reactions and microstructure on long-term experimental fault zone weakening

NASA Astrophysics Data System (ADS)

Niemeijer, Andre R.

2017-04-01

The frictional properties of fault rocks and, in particular, the velocity dependence of friction and associated rate-and-state parameters, are thought to exert an important control on earthquake nucleation and propagation. Experimental results obtained from natural fault gouges typically show that the velocity dependence of friction is a function of both temperature and sliding velocity, indicating that thermally activated time-dependent processes are fundamentally responsible for causing velocity-weakening behavior in silicate-bearing gouges at earthquake "nucleation velocities" (˜ 1 μm/s) and temperatures around 150-300 ˚ C. In addition, slow experiments at velocities of 10s of nm/s using three different fault gouge types all exhibit major weakening with ongoing displacement at constant velocity. Microstructural and microanalytical analyses demonstrate that the development of a weak through-going foliation as well as the (shear-enhanced) formation of new, weak minerals such as talc or muscovite occurred, which both presumably contributed to the observed weakening. Importantly, the slow deformation rates allow for time-dependent viscous deformation (e.g. pressure solution) to occur at low shear stress within the hard, frictionally strong minerals such as quartz. The results highlight the importance of the chemical effects of fluids and microstructural development on long-term fault weakening under slow loading conditions. The resultant frictionally weak fault gouges allow strain to remain localized, yield a strong permeability anisotropy and provide a barrier for rupture propagation. Along-fault variations in the chemical conditions thus have the potential to produce strong contrasts in frictional properties, which can have a large effect on potential earthquake rupture size and style.

Subcritical fracture propagation in rocks: An examination using the methods of fracture mechanics and non-destructive testing. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Swanson, P. L.

1984-01-01

An experimental investigation of tensile rock fracture is presented with an emphasis on characterizing time dependent crack growth using the methods of fracture mechanics. Subcritical fracture experiments were performed in moist air on glass and five different rock types at crack velocities using the double torsion technique. The experimental results suggest that subcritical fracture resistance in polycrystals is dominated by microstructural effects. Evidence for gross violations of the assumptions of linear elastic fracture mechanics and double torsion theory was found in the tests on rocks. In an effort to obtain a better understanding of the physical breakdown processes associated with rock fracture, a series of nondestructive evaluation tests were performed during subcritical fracture experiments on glass and granite. Comparison of the observed process zone shape with that expected on the basis of a critical normal principal tensile stress criterion shows that the zone is much more elongated in the crack propagation direction than predicted by the continuum based microcracking model alone.

Electroosmotic pump performance is affected by concentration polarizations of both electrodes and pump

PubMed Central

Suss, Matthew E.; Mani, Ali; Zangle, Thomas A.; Santiago, Juan G.

2010-01-01

Current methods of optimizing electroosmotic (EO) pump performance include reducing pore diameter and reducing ionic strength of the pumped electrolyte. However, these approaches each increase the fraction of total ionic current carried by diffuse electric double layer (EDL) counterions. When this fraction becomes significant, concentration polarization (CP) effects become important, and traditional EO pump models are no longer valid. We here report on the first simultaneous concentration field measurements, pH visualizations, flow rate, and voltage measurements on such systems. Together, these measurements elucidate key parameters affecting EO pump performance in the CP dominated regime. Concentration field visualizations show propagating CP enrichment and depletion fronts sourced by our pump substrate and traveling at order mm/min velocities through millimeter-scale channels connected serially to our pump. The observed propagation in millimeter-scale channels is not explained by current propagating CP models. Additionally, visualizations show that CP fronts are sourced by and propagate from the electrodes of our system, and then interact with the EO pump-generated CP zones. With pH visualizations, we directly detect that electrolyte properties vary sharply across the anode enrichment front interface. Our observations lead us to hypothesize possible mechanisms for the propagation of both pump- and electrode-sourced CP zones. Lastly, our experiments show the dynamics associated with the interaction of electrode and membrane CP fronts, and we describe the effect of these phenomena on EO pump flow rates and applied voltages under galvanostatic conditions. PMID:21516230

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yu; Gao, Kai; Huang, Lianjie

Accurate imaging and characterization of fracture zones is crucial for geothermal energy exploration. Aligned fractures within fracture zones behave as anisotropic media for seismic-wave propagation. The anisotropic properties in fracture zones introduce extra difficulties for seismic imaging and waveform inversion. We have recently developed a new anisotropic elastic-waveform inversion method using a modified total-variation regularization scheme and a wave-energy-base preconditioning technique. Our new inversion method uses the parameterization of elasticity constants to describe anisotropic media, and hence it can properly handle arbitrary anisotropy. We apply our new inversion method to a seismic velocity model along a 2D-line seismic data acquiredmore » at Eleven-Mile Canyon located at the Southern Dixie Valley in Nevada for geothermal energy exploration. Our inversion results show that anisotropic elastic-waveform inversion has potential to reconstruct subsurface anisotropic elastic parameters for imaging and characterization of fracture zones.« less

A novel EBSD-based finite-element wave propagation model for investigating seismic anisotropy: Application to Finero Peridotite, Ivrea-Verbano Zone, Northern Italy

NASA Astrophysics Data System (ADS)

Zhong, Xin; Frehner, Marcel; Kunze, Karsten; Zappone, Alba

2014-10-01

A novel electron backscatter diffraction (EBSD) -based finite-element (FE) wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples. The FE model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2D EBSD sections. The numerical model allows separation of the effects of crystallographic preferred orientation (CPO) and shape preferred orientation (SPO). The obtained seismic velocities with respect to specimen orientation are compared with Voigt-Reuss-Hill estimates and with laboratory measurements. The results of these three independent methods testify that CPO is the dominant factor controlling seismic anisotropy. Fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large (up to 23%). The SPO influence is minor compared to the other factors. The presented FE model is discussed with regard to its potential in simulating seismic wave propagation using EBSD data representing natural rock petrofabrics.

Finite-frequency sensitivity kernels for head waves

NASA Astrophysics Data System (ADS)

Zhang, Zhigang; Shen, Yang; Zhao, Li

2007-11-01

Head waves are extremely important in determining the structure of the predominantly layered Earth. While several recent studies have shown the diffractive nature and the 3-D Fréchet kernels of finite-frequency turning waves, analogues of head waves in a continuous velocity structure, the finite-frequency effects and sensitivity kernels of head waves are yet to be carefully examined. We present the results of a numerical study focusing on the finite-frequency effects of head waves. Our model has a low-velocity layer over a high-velocity half-space and a cylindrical-shaped velocity perturbation placed beneath the interface at different locations. A 3-D finite-difference method is used to calculate synthetic waveforms. Traveltime and amplitude anomalies are measured by the cross-correlation of synthetic seismograms from models with and without the velocity perturbation and are compared to the 3-D sensitivity kernels constructed from full waveform simulations. The results show that the head wave arrival-time and amplitude are influenced by the velocity structure surrounding the ray path in a pattern that is consistent with the Fresnel zones. Unlike the `banana-doughnut' traveltime sensitivity kernels of turning waves, the traveltime sensitivity of the head wave along the ray path below the interface is weak, but non-zero. Below the ray path, the traveltime sensitivity reaches the maximum (absolute value) at a depth that depends on the wavelength and propagation distance. The sensitivity kernels vary with the vertical velocity gradient in the lower layer, but the variation is relatively small at short propagation distances when the vertical velocity gradient is within the range of the commonly accepted values. Finally, the depression or shoaling of the interface results in increased or decreased sensitivities, respectively, beneath the interface topography.

A surface wave reflector in Southwestern Japan

NASA Astrophysics Data System (ADS)

Mak, S.; Koketsu, K.; Miyake, H.; Obara, K.; Sekine, S.

2009-12-01

Surface waves at short periods (<35s) are affected severely by heterogeneities in the crust and the uppermost mantle. When the scale of heterogeneity is sufficiently large, its effect can be studied in a deterministic way using conventional concepts of reflection and refraction. A well-known example is surface wave refraction at continental margin. We present a case study to investigate the composition of surface wave coda in a deterministic approach. A long duration of surface wave coda with a predominant period of 20s is observed during various strong earthquakes around Japan. The coda shows an unambiguous propagation direction, implying a deterministic nature. Beamforming and particle motion analysis suggest that the surface wave later arrivals could be explained by Love wave reflections by a point reflector located at offshore southeast to Kyushu. The reflection demonstrates a seemingly incidence-independent favorable azimuth in emitting strength. In additional to beamforming, we use a new regional crustal velocity model to perform a grid-search ray-tracing with the assumption of point reflector to further constrain to location of coda generation. Because strong velocity anomalies exist near the zone of interest, we decide to use a network shortest-path ray-tracing method, instead of analytical methods like shooting and bending, to avoid the problems like convergence, shadow zone, and smooth model assumption. Two geological features are found to be related to the formation of the coda. The primary one is the intersection between the Kyushu-Palau Ridge and the Nankai Trough at offshore southeast to Kyushu (hereafter referred as "KPR-NT"), which may act as a point reflector. There is a strong Love wave phase velocity anomaly at KPR-NT but not other parts of the ridge, implying that topography is irrelevant. Rayleigh wave phase velocity does not experience a strong anomaly there, which is consistent to the absence of Rayleigh wave reflections implied by the observed particle motions. The secondary one is a low phase velocity (<2km/s for T=20s) at the accretionary wedge of the Nankai Trough due to the thick sediment. Such a long and narrow low velocity zone, with its southwest tip at KPR-NT, is a potential wave-guide to channel waves towards KPR-NT. The longer duration of deterministic later arrivals than the direct arrival is partially explained by multi-pathing due to the wave-guide. The surface wave coda is observable for earthquakes whose propagation path does not include the accretionary wedge, implying that the wedge is an enhancer but not indispensable of the formation of the observed coda.

Earthquake rupture dynamics in poorly lithified sediments

NASA Astrophysics Data System (ADS)

De Paola, N.; Bullock, R. J.; Holdsworth, R.; Marco, S.; Nielsen, S. B.

2017-12-01

Several recent large earthquakes have generated anomalously large slip patches when propagating through fluid-saturated, clay-rich sediments near the surface. Friction experiments at seismic slip rates show that such sediments are extremely weak and deform with very little energy dissipation, which facilitates rupture propagation. Although dynamic weakening may explain the ease of rupture propagation through such sediments, it cannot account for the peculiar slow rupture velocity and low radiation efficiency exhibited by some large, shallow ruptures. Here, we integrate field and experimental datasets to describe on- and off-fault deformation in natural syn-depositional seismogenic faults (< 35 ka) in shallow, clay-rich, poorly lithified sediments from the Dead Sea Fault system, Israel. The data are then used to estimate the energy dissipated by on- and off-fault damage during earthquake rupture through shallow, clay-rich sediments. Our mechanical and field data show localised principal slip zones (PSZs) that deform by particulate flow, with little energy dissipated by brittle fracturing with cataclasis. Conversely, we show that coseismic brittle and ductile deformation in the damage zones outwith the PSZ, which cannot be replicated in small-scale laboratory experiments, is a significant energy sink, contributing to an energy dissipation that is one order of magnitude greater than that estimated from laboratory experiments alone. In particular, a greater proportion of dissipated energy would result in lower radiation efficiency, due to a reduced proportion of radiated energy, plus slower rupture velocity and more energy radiation in the low frequency range than might be anticipated from laboratory experiments alone. This result is in better agreement with seismological estimates of fracture energy, implying that off-fault damage can account for the geophysical characteristics of earthquake ruptures as they pass through clay-rich sediments in the shallow crust.

An experimental study of combustion: The turbulent structure of a reacting shear layer formed at a rearward-facing step. Ph.D. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Pitz, R. W.

1981-01-01

A premixed propane-air flame is stabilized in a turbulent free shear layer formed at a rearward-facing step. The mean and rms averages of the turbulent velocity flow field were determined by LDV for both reacting and non-reacting flows. The reaching flow was visualized by high speed schlieren photography. Large scale structures dominate the reacting shear layer. The growth of the large scale structures is tied to the propagation of the flame. The linear growth rate of the reacting shear layer defined by the mean velocity profiles is unchanged by combustion but the virtual origin is shifted downstream. The reacting shear layer based on the mean velocity profiles is shifted toward the recirculation zone and the reattachments lengths are shortened by 30%.

Cumulative co-seismic fault damage and feedbacks on earthquake rupture

NASA Astrophysics Data System (ADS)

Mitchell, T. M.; Aben, F. M.; Ostermeijer, G.; Rockwell, T. K.; Doan, M. L.

2017-12-01

The importance of the damage zone in the faulting and earthquake process is widely recognized, but our understanding of how damage zones are created, what their properties are, and how they feed back into the seismic cycle, is remarkably poorly known. Firstly, damaged rocks have reduced elastic moduli, cohesion and yield strength, which can cause attenuation and potentially non-linear wave propagation effects during ruptures. Secondly, damaged fault rocks are generally more permeable than intact rocks, and hence play a key role in the migration of fluids in and around fault zones over the seismic cycle. Finally, the dynamic generation of damage as the earthquake propagates can itself influence the dynamics of rupture propagation, by increasing the amount of energy dissipation, decreasing the rupture velocity, modifying the size of the earthquake, changing the efficiency of weakening mechanisms such as thermal pressurisation of pore fluids, and even generating seismic waves itself . All of these effects imply that a feedback exists between the damage imparted immediately after rupture propagation, at the early stages of fault slip, and the effects of that damage on subsequent ruptures dynamics. In recent years, much debate has been sparked by the identification of so-called `pulverized rocks' described on various crustal-scale faults, a type of intensely damaged fault rock which has undergone minimal shear strain, and the occurrence of which has been linked to damage induced by transient high strain-rate stress perturbations during earthquake rupture. Damage induced by such transient stresses, whether compressional or tensional, likely constitute heterogeneous modulations of the remote stresses that will impart significant changes on the strength, elastic and fluid flow properties of a fault zone immediately after rupture propagation, at the early stage of fault slip. In this contribution, we will demonstrate laboratory and field examples of two dynamic mechanisms that have been proposed for the generation of pulverized rocks; (i) compressive loading by high-frequency stress pulses due to the radiation of seismic waves and (ii) explosive dilation in tension in rocks containing pressurized pore fluids.

New Analysis Scheme of Flow-Acoustic Coupling for Gas Ultrasonic Flowmeter with Vortex near the Transducer.

PubMed

Sun, Yanzhao; Zhang, Tao; Zheng, Dandan

2018-04-10

Ultrasonic flowmeters with a small or medium diameter are widely used in process industries. The flow field disturbance on acoustic propagation caused by a vortex near the transducer inside the sensor as well as the mechanism and details of flow-acoustic interaction are needed to strengthen research. For that reason, a new hybrid scheme is proposed; the theories of computational fluid dynamics (CFD), wave acoustics, and ray acoustics are used comprehensively by a new step-by-step method. The flow field with a vortex near the transducer, and its influence on sound propagation, receiving, and flowmeter performance are analyzed in depth. It was found that, firstly, the velocity and vortex intensity distribution were asymmetric on the sensor cross-section and acoustic path. Secondly, when passing through the vortex zone, the central ray trajectory was deflected significantly. The sound pressure on the central line of the sound path also changed. Thirdly, the pressure deviation becomes larger with as the flow velocity increases. The deviation was up to 17% for different velocity profiles in a range of 0.6 m/s to 53 m/s. Lastly, in comparison to the theoretical value, the relative deviation of the instrument coefficient for the velocity profile with a vortex near the transducer reached up to -17%. In addition, the rationality of the simulation was proved by experiments.

New Analysis Scheme of Flow-Acoustic Coupling for Gas Ultrasonic Flowmeter with Vortex near the Transducer

PubMed Central

Zhang, Tao; Zheng, Dandan

2018-01-01

Ultrasonic flowmeters with a small or medium diameter are widely used in process industries. The flow field disturbance on acoustic propagation caused by a vortex near the transducer inside the sensor as well as the mechanism and details of flow-acoustic interaction are needed to strengthen research. For that reason, a new hybrid scheme is proposed; the theories of computational fluid dynamics (CFD), wave acoustics, and ray acoustics are used comprehensively by a new step-by-step method. The flow field with a vortex near the transducer, and its influence on sound propagation, receiving, and flowmeter performance are analyzed in depth. It was found that, firstly, the velocity and vortex intensity distribution were asymmetric on the sensor cross-section and acoustic path. Secondly, when passing through the vortex zone, the central ray trajectory was deflected significantly. The sound pressure on the central line of the sound path also changed. Thirdly, the pressure deviation becomes larger with as the flow velocity increases. The deviation was up to 17% for different velocity profiles in a range of 0.6 m/s to 53 m/s. Lastly, in comparison to the theoretical value, the relative deviation of the instrument coefficient for the velocity profile with a vortex near the transducer reached up to −17%. In addition, the rationality of the simulation was proved by experiments. PMID:29642577

Lidar Observations of Wave Shape

NASA Astrophysics Data System (ADS)

Brodie, K. L.; Raubenheimer, B.; Spore, N.; Gorrell, L.; Slocum, R. K.; Elgar, S.

2016-02-01

As waves propagate across the inner-surf zone, through a shorebreak, to the swash, their shapes can evolve rapidly, particularly if there are large changes in water depth over a wavelength. As wave shapes evolve, the time history of near-bed wave-orbital velocities also changes. Asymmetrical near-bed velocities result in preferential directions for sediment transport, and spatial variations in asymmetries can lead to morphological evolution. Thus, understanding and predicting wave shapes in the inner-surf and swash zones is important to improving sediment transport predictions. Here, rapid changes in wave shape, quantified by 3rd moments (skewness and asymmetry) of the sea-surface elevation time series, were observed on a sandy Atlantic Ocean beach near Duck, NC using terrestrial lidar scanners that measure the elevation of the water surface along a narrow cross-shore transect with high spatial [O(1 cm)] and temporal [O(0.5 s)] resolution. The terrestrial lidar scanners were mounted on a tower on the beach dune (about 8 m above the water surface) and on an 8-m tall amphibious tripod [the Coastal Research Amphibious Buggy (CRAB)]. Observations with the dune lidar are used to investigate how bulk wave shape parameters such as wave skewness and asymmetry, and the ratio of wave height to water depth (gamma) vary with beach slope, tide level, and offshore wave conditions. Observations with the lidar mounted on the CRAB are used to investigate the evolution of individual waves propagating across the surf zone and shorebreak to the swash. For example, preliminary observations from the CRAB include a wave that appeared to shoal and then "pitch" backwards immediately prior to breaking and running up the beach. Funded by the USACE Coastal Field Data Collection Program, ASD(R&E), and ONR.

The Electrical Network of Maize Root Apex is Gravity Dependent

PubMed Central

Masi, Elisa; Ciszak, Marzena; Comparini, Diego; Monetti, Emanuela; Pandolfi, Camilla; Azzarello, Elisa; Mugnai, Sergio; Baluška, Frantisek; Mancuso, Stefano

2015-01-01

Investigations carried out on maize roots under microgravity and hypergravity revealed that gravity conditions have strong effects on the network of plant electrical activity. Both the duration of action potentials (APs) and their propagation velocities were significantly affected by gravity. Similarly to what was reported for animals, increased gravity forces speed-up APs and enhance synchronized electrical events also in plants. The root apex transition zone emerges as the most active, as well as the most sensitive, root region in this respect. PMID:25588706

The electrical network of maize root apex is gravity dependent.

PubMed

Masi, Elisa; Ciszak, Marzena; Comparini, Diego; Monetti, Emanuela; Pandolfi, Camilla; Azzarello, Elisa; Mugnai, Sergio; Baluška, Frantisek; Mancuso, Stefano

2015-01-15

Investigations carried out on maize roots under microgravity and hypergravity revealed that gravity conditions have strong effects on the network of plant electrical activity. Both the duration of action potentials (APs) and their propagation velocities were significantly affected by gravity. Similarly to what was reported for animals, increased gravity forces speed-up APs and enhance synchronized electrical events also in plants. The root apex transition zone emerges as the most active, as well as the most sensitive, root region in this respect.

High-resolution Imaging of the Philippine Sea Plate subducting beneath Central Japan

NASA Astrophysics Data System (ADS)

Padhy, S.; Furumura, T.

2016-12-01

Thermal models predict that the oceanic crust of the young (<20 Ma) and warmer Philippine-sea plate (PHP) is more prone to melting. Deriving a high-resolution image of the PHP, including slab melting and other features of the subduction zone, is a key to understand the basics of earthquake occurrence and origin of magma in complex subduction zone like central Japan, where both the PHP and Pacific (PAC) Plates subduct. To this purpose, we analyzed high-resolution waveforms of moderate sized (M 4-6), intermediate-to-deep (>150 km) PAC earthquakes occurring in central Japan and conducted numerical simulation to derive a fine-scale PHP model, which is not constrained in earlier studies. Observations show spindle-shaped seismograms with strong converted phases and extended coda with very slow decay from a group of PAC events occurring in northern part of central Japan and recorded by high-sensitivity seismograph network (Hi-net) stations in the region. We investigate the mechanism of propagation of these anomalous waveforms using the finite difference method (FDM) simulation of wave propagation through the subduction zone. We examine the effects on waveform changes of major subduction zone features, such as the melting of oceanic crust in PHP, serpentinized mantle wedge, hydrated layer on the PAC due to slab dehydration, and anomaly in upper mantle between the PAC and PHP. Simulation results show that the waveform anomaly is primarily explained by strong scattering and absorption of high-frequency energy by the low-velocity anomalous mantle structure, with a strong coda excitation yielding spindle-shaped waveforms. The data are secondarily explained by melting of PHP in the basaltic crust. The location of the mantle anomaly is tightly constrained by the observation and evidence of PAC thinning in the region; these localized low-velocity structures aid in ascending the slab-derived fluids around the slab thinning. We expect that the results of this study will enhance our present understanding on the mechanism of intermediate to deep earthquakes in the region.

Strong seismic wave scattering beneath Kanto region derived from dense K-NET/KiK-net strong motion network and numerical simulation

NASA Astrophysics Data System (ADS)

Takemura, S.; Yoshimoto, K.

2013-12-01

Observed seismograms, which consist of the high-frequency body waves through the low-velocity (LV) region at depth of 20-40 km beneath northwestern Chiba in Kanto, show strong peak delay and spindle shape of S waves. By analyzing dense seismic records from K-NET/KiK-net, such spindle-shape S waves are clearly observed in the frequency range of 1-8 Hz. In order to investigate a specific heterogeneous structure to generate such observations, we conduct 3-D finite-difference method (FDM) simulation using realistic heterogeneous models and compare the simulation results with dense strong motion array observations. Our 3-D simulation model is covering the zone 150 km by 64 km in horizontal directions and 75 km in vertical direction, which has been discretized with uniform grid size 0.05 km. We assume a layered background velocity structure, which includes basin structure, crust, mantle and subducting oceanic plate, base on the model proposed by Koketsu et al. (2008). In order to introduce the effect of seismic wave scattering, we assume a stochastic random velocity fluctuation in each layer. Random velocity fluctuations are characterized by exponential-type auto-correlation function (ACF) with correlation distance a = 3 km and rms value of fluctuation e = 0.05 in the upper crust, a = 3 km and e = 0.07 in the lower crust, a = 10 km and e = 0.02 in the mantle. In the subducting oceanic plate, we assume an anisotropic random velocity fluctuation characterized by exponential-type ACF with aH = 10 km in horizontal direction, aZ = 0.5 km in vertical direction and e = 0.02 (e.g., Furumura and Kennett, 2005). In addition, we assume a LV zone at northeastern part of Chiba with depth of 20-40 km (e.g., Matsubara et al., 2004). In the LV zone, random velocity fluctuation characterized by Gaussian-type ACF with a = 1 km and e = 0.07 is superposed on exponential-type ACF with a = 3 km and e = 0.07, in order to modulate the S-wave propagation in the dominant frequency range of spindle-shape S waves. Such large-scale FDM simulations are conducted on the Earth Simulator at JAMSTEC. It is found that the FDM simulation of the model without strong velocity fluctuation cannot explain the characteristics of observed S waves. By introducing strong velocity fluctuation in the LV zone, strong peak delay and spindle-shape S waves observed at central and southern part of Chiba are simulated successfully. In addition, the strong amplitude decrease of S waves in the LV zone due to strong seismic scattering is good corresponding to results based on the tomographic study of Q in Kanto (e.g., Nakamura et al., 2006). Simulation results demonstrated that strong velocity fluctuation in the LV zone plays important role in the peak delay and waveform shape. The LV zone beneath northeastern Chiba is considered as a result of dehydration from oceanic crust of subducted Philippine Sea plate (e.g., Matsubara et al., 2005). Therefore strong small-scale velocity fluctuation in the LV zone may be related with dehydrated water.

Modelling the average velocity of propagation of the flame front in a gasoline engine with hydrogen additives

NASA Astrophysics Data System (ADS)

Smolenskaya, N. M.; Smolenskii, V. V.

2018-01-01

The paper presents models for calculating the average velocity of propagation of the flame front, obtained from the results of experimental studies. Experimental studies were carried out on a single-cylinder gasoline engine UIT-85 with hydrogen additives up to 6% of the mass of fuel. The article shows the influence of hydrogen addition on the average velocity propagation of the flame front in the main combustion phase. The dependences of the turbulent propagation velocity of the flame front in the second combustion phase on the composition of the mixture and operating modes. The article shows the influence of the normal combustion rate on the average flame propagation velocity in the third combustion phase.

The architecture and frictional properties of faults in shale

NASA Astrophysics Data System (ADS)

De Paola, Nicola; Murray, Rosanne; Stillings, Mark; Imber, Jonathan; Holdsworth, Robert

2015-04-01

The geometry of brittle fault zones and associated fracture patterns in shale rocks, as well as their frictional properties at reservoir conditions, are still poorly understood. Nevertheless, these factors may control the very low recovery factors (25% for gas and 5% for oil) obtained during fracking operations. Extensional brittle fault zones (maximum displacement ≤ 3 m) cut exhumed oil mature black shales in the Cleveland Basin (UK). Fault cores up to 50 cm wide accommodated most of the displacement, and are defined by a stair-step geometry, controlled by the reactivation of en-echelon, pre-existing joints in the protolith. Cores typically show a poorly developed damage zone, up to 25 cm wide, and sharp contact with the protolith rocks. Their internal architecture is characterised by four distinct fault rock domains: foliated gouges; breccias; hydraulic breccias; and a slip zone up to 20 mm thick, composed of a fine-grained black gouge. Hydraulic breccias are located within dilational jogs with aperture of up to 20 cm, composed of angular clasts of reworked fault and protolith rock, dispersed within a sparry calcite cement. Velocity-step and slide-hold-slide experiments at sub-seismic slip rates (microns/s) were performed in a rotary shear apparatus under dry, water and brine-saturated conditions, for displacements of up to 46 cm. Both the protolith shale and the slip zone black gouge display shear localization, velocity strengthening behaviour and negative healing rates. Experiments at seismic slip rates (1.3 m/s), performed on the same materials under dry conditions, show that after initial friction values of 0.5-0.55, friction decreases to steady-state values of 0.1-0.15 within the first 10 mm of slip. Contrastingly, water/brine saturated gouge mixtures, exhibit almost instantaneous attainment of very low steady-state sliding friction (0.1). Our field observations show that brittle fracturing and cataclastic flow are the dominant deformation mechanisms in the fault core of shale faults, where slip localization may lead to the development of a thin slip zone made of very fine-grained gouges. The velocity-strengthening behaviour and negative healing rates observed during our laboratory experiments, suggest that slow, stable sliding faulting should take place within the protolith rocks and slip zone gouges. This behaviour will cause slow fault/fracture propagation, affecting the rate at which new fracture areas are created and, hence, limiting oil and gas production during reservoir stimulation. During slipping events, fluid circulation may be very effective along the fault zone at dilational jogs - where oil and gas production should be facilitated by the creation of large fracture areas - and rather restricted in the adjacent areas of the protolith, due to the lack of a well-developed damage zone and the low permeability of the matrix and slip zone gouge. Finally, our experiments performed at seismic slip rates show that seismic ruptures may still be able to propagate in a very efficient way within the slip zone of fluid-saturated shale faults, due to the attainment of instantaneous weakening.

Penny-shaped crack propagation in spallation of Zr-BMGs

NASA Astrophysics Data System (ADS)

Ling, Z.; Huang, X.; Dai, L. H.

2015-09-01

Typical penny-shaped microcracks at their propagating in spallation of Zr-based bulk metallic glass (Zr-BMG) samples were captured by a specially designed plate impact technique. Based on the morphology and stress environment of the microcrack, a damaged zone or propagation zone around the crack tips, similar to the cohesive zone in classical fracture theories, is applied. Especially the scale of such a damaged zone represents a scale of the crack propagation. Its fast propagation would quickly bring a longer crack or cause cracks coalesce to form another longer one. The estimated propagation scales of microcracks are reasonable compared with what occurred in the Zr-BMG samples.

Validation and Performance Comparison of Numerical Codes for Tsunami Inundation

NASA Astrophysics Data System (ADS)

Velioglu, D.; Kian, R.; Yalciner, A. C.; Zaytsev, A.

2015-12-01

In inundation zones, tsunami motion turns from wave motion to flow of water. Modelling of this phenomenon is a complex problem since there are many parameters affecting the tsunami flow. In this respect, the performance of numerical codes that analyze tsunami inundation patterns becomes important. The computation of water surface elevation is not sufficient for proper analysis of tsunami behaviour in shallow water zones and on land and hence for the development of mitigation strategies. Velocity and velocity patterns are also crucial parameters and have to be computed at the highest accuracy. There are numerous numerical codes to be used for simulating tsunami inundation. In this study, FLOW 3D and NAMI DANCE codes are selected for validation and performance comparison. Flow 3D simulates linear and nonlinear propagating surface waves as well as long waves by solving three-dimensional Navier-Stokes (3D-NS) equations. FLOW 3D is used specificaly for flood problems. NAMI DANCE uses finite difference computational method to solve linear and nonlinear forms of shallow water equations (NSWE) in long wave problems, specifically tsunamis. In this study, these codes are validated and their performances are compared using two benchmark problems which are discussed in 2015 National Tsunami Hazard Mitigation Program (NTHMP) Annual meeting in Portland, USA. One of the problems is an experiment of a single long-period wave propagating up a piecewise linear slope and onto a small-scale model of the town of Seaside, Oregon. Other benchmark problem is an experiment of a single solitary wave propagating up a triangular shaped shelf with an island feature located at the offshore point of the shelf. The computed water surface elevation and velocity data are compared with the measured data. The comparisons showed that both codes are in fairly good agreement with each other and benchmark data. All results are presented with discussions and comparisons. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement No 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe)

Fabric changes and their influence on P-wave velocity patterns—examples from a polyphase deformed orthogneiss

NASA Astrophysics Data System (ADS)

Siegesmund, S.; Vollbrecht, A.; Pros, Z.

1993-10-01

The complete P-wave velocity distribution, preferred orientation of rock-forming minerals and microcracks of two differently deformed orthogneisses from the Kutna Hora Crystalline Unit were investigated. The complete symmetry of P-wave velocities were determined as a function of confining pressure on the basis of 132 independent propagation directions up to 400 MPa. The two samples are of almost identical mineralogical composition, but exhibit different fabrics which can be related to different positions within a large-scale fold structure. The symmetry of the Vp-diagrams change from nearly transversely isotropic for the sample from the limb area to orthorhombic for the sample from the hinge zone, which shows an additional crenulation cleavage. This change of symmetry is observed at all pressure levels. Reorientation of the main velocity directions ( Vpmin, Vpmax, Kpint) between hinge and limb is controlled by the microcrack fabric and the texture of the rock-forming minerals. This can cause significant differences in reflectivity related to fabric changes within large-scale folds.

Electromechanical wave imaging and electromechanical wave velocity estimation in a large animal model of myocardial infarction.

PubMed

Costet, Alexandre; Melki, Lea; Sayseng, Vincent; Hamid, Nadira; Nakanishi, Koki; Wan, Elaine; Hahn, Rebecca; Homma, Shunichi; Konofagou, Elisa

2017-11-29

Echocardiography is often used in the clinic for detection and characterization of myocardial infarction. Electromechanical wave imaging (EWI) is a non-invasive ultrasound-based imaging technique based on time-domain incremental motion and strain estimation that can evaluate changes in contractility in the heart. In this study, electromechanical activation is assessed in infarcted heart to determine whether EWI is capable of detecting and monitoring infarct formation. Additionally, methods for estimating electromechanical wave (EW) velocity are presented, and changes in the EW propagation velocity after infarct formation are studied. Five (n  =  5) adult mongrels were used in this study. Successful infarct formation was achieved in three animals by ligation of the left anterior descending (LAD) coronary artery. Dogs were survived for a few days after LAD ligation and monitored daily with EWI. At the end of the survival period, dogs were sacrificed and TTC (tetrazolium chloride) staining confirmed the formation and location of the infarct. In all three dogs, as soon as day 1 EWI was capable of detecting late-activated and non-activated regions, which grew over the next few days. On final day images, the extent of these regions corresponded to the location of infarct as confirmed by staining. EW velocities in border zones of infarct were significantly lower post-infarct formation when compared to baseline, whereas velocities in healthy tissues were not. These results indicate that EWI and EW velocity might help with the detection of infarcts and their border zones, which may be useful for characterizing arrhythmogenic substrate.

Electromechanical wave imaging and electromechanical wave velocity estimation in a large animal model of myocardial infarction

NASA Astrophysics Data System (ADS)

Costet, Alexandre; Melki, Lea; Sayseng, Vincent; Hamid, Nadira; Nakanishi, Koki; Wan, Elaine; Hahn, Rebecca; Homma, Shunichi; Konofagou, Elisa

2017-12-01

Echocardiography is often used in the clinic for detection and characterization of myocardial infarction. Electromechanical wave imaging (EWI) is a non-invasive ultrasound-based imaging technique based on time-domain incremental motion and strain estimation that can evaluate changes in contractility in the heart. In this study, electromechanical activation is assessed in infarcted heart to determine whether EWI is capable of detecting and monitoring infarct formation. Additionally, methods for estimating electromechanical wave (EW) velocity are presented, and changes in the EW propagation velocity after infarct formation are studied. Five (n  =  5) adult mongrels were used in this study. Successful infarct formation was achieved in three animals by ligation of the left anterior descending (LAD) coronary artery. Dogs were survived for a few days after LAD ligation and monitored daily with EWI. At the end of the survival period, dogs were sacrificed and TTC (tetrazolium chloride) staining confirmed the formation and location of the infarct. In all three dogs, as soon as day 1 EWI was capable of detecting late-activated and non-activated regions, which grew over the next few days. On final day images, the extent of these regions corresponded to the location of infarct as confirmed by staining. EW velocities in border zones of infarct were significantly lower post-infarct formation when compared to baseline, whereas velocities in healthy tissues were not. These results indicate that EWI and EW velocity might help with the detection of infarcts and their border zones, which may be useful for characterizing arrhythmogenic substrate.

Mechanical Erosion of the Seismogenic Zone by Creep from below on Rate-State Faults

NASA Astrophysics Data System (ADS)

Werner, M. J.; Rubin, A. M.

2012-12-01

The aim of this study is to increase our understanding of how earthquakes nucleate on frictionally-locked fault patches that are loaded by the growing stress concentrations at their boundaries due to aseismic creep. Such mechanical erosion from below of locked patches has previously been invoked by Gillard et al. (1996) to explain accelerating seismicity and increases in maximum earthquake magnitude on a strike-slip streak (a narrow ribbon of tightly clustered seismicity) in Kilauea's East rift, and it might also play a role in the loading of major locked strike-slip faults by creep from below the seismogenic zone. Gillard et al. (1996) provided simple analytical estimates of the size of and of the time-dependence of the moment release within the eroding edge of the locked zone that matched observed seismicity in Kilauea's East rift. However, an obvious, similar signal has not consistently been found before major strike-slip earthquakes on presumably analogous faults. Here, we use simulations to determine to what extent the simple estimates by Gillard et al. survive a wider range of geometric configurations, friction laws and slip histories. We model the boundary between the locked and creeping sections at the base of the seismogenic zone as a transition between steady-state velocity-strengthening behavior at greater depth to velocity-weakening at shallow depth, qualitatively consistent with laboratory estimates of the temperature dependence of (a-b). As we increase the ratio of the size H of the velocity-weakening region over the nucleation length scale L∞ [Rubin & Ampuero, 2005] from tens to more appropriate hundreds and thousands in our 1D model, we observe an increasing number of creep fronts that march into the seismogenic zone from the weakening/strengthening transition between surface-rupturing seismic events. For moderate to large ratios of H/L∞ , these fronts begin to appear while afterslip from large events is still propagating down-dip below the transition and reloading the seismogenic zone near the transition. Some creep fronts slow down and fail, especially during very early deep afterslip, while later creep fronts tend to accelerate to seismic speeds (modeled using radiation-damping) after traveling a distance above the transition that appears to be controlled by L∞ . The ensuing earthquakes propagate updip and reach only a fraction of the seismogenic height, until eventually a surface-rupturing event occurs. As we increase a/b towards 1 in the velocity-weakening zone, we observe some large events nucleating well above the transition at stress concentrations left over from earlier seismic events that did not reach the surface. In our simulations thus far, total moment release rates over the earthquake cycle tend to decay with afterslip, occasionally punctuated by the smaller earthquakes, which decrease in frequency over the cycle and seem mostly driven by deep afterslip. It thus appears possible that, at least on homogeneous (aging) rate-state faults, post-seismic afterslip is masking (some of) the seismicity patterns expected from Gillard et al.'s analysis, although a wider range of simulations is warranted.

Simulating the Evolving Behavior of Secondary Slow Slip Fronts

NASA Astrophysics Data System (ADS)

Peng, Y.; Rubin, A. M.

2017-12-01

High-resolution tremor catalogs of slow slip events reveal secondary slow slip fronts behind the main front that repetitively occupy the same source area during a single episode. These repetitive fronts are most often observed in regions with high tremor density. Their recurrence intervals gradually increase from being too short to be tidally modulated (tens of minutes) to being close to tidal periods (about 12 or 24 hours). This could be explained by a decreasing loading rate from creep in the surrounding regions (with few or no observable tremor events) as the main front passes by. As the recurrence intervals of the fronts increase, eventually they lock in on the tidal periods. We attempt to simulate this numerically using a rate-and-state friction law that transitions from velocity-weakening at low slip speeds to velocity strengthening at high slip speeds. Many small circular patches with a cutoff velocity an order of magnitude higher than that of the background are randomly placed on the fault, in order to simulate the average properties of the high-density tremor zone. Preliminary results show that given reasonable parameters, this model produces similar propagation speeds of the forward-migrating main front inside and outside the high-density tremor zone, consistent with observations. We will explore the behavior of the secondary fronts that arise in this model, in relation to the local density of the small tremor-analog patches, the overall geometry of the tremor zone and the tides.

Incorporating fault zone head wave and direct wave secondary arrival times into seismic tomography: Application at Parkfield, California

NASA Astrophysics Data System (ADS)

Bennington, N. L.; Thurber, C. H.; Zhang, H.; Peng, Z.; Zhao, P.

2011-12-01

Large crustal faults such as the San Andreas fault (SAF) often juxtapose rocks of significantly different elastic properties, resulting in well-defined bimaterial interfaces. A sharp material contrast across the fault interface is expected to generate fault zone head waves (FZHW's) that spend a large portion of their propagation paths refracting along the bimaterial interface (Ben-Zion 1989, 1990; Ben-Zion & Aki 1990). Because of this FZHW's provide a high-resolution tool for imaging the velocity contrast across the fault. Recently, Zhao et al. (2010) systematically analyzed large data sets of near-fault waveforms recorded by several permanent and temporary seismic networks along the Parkfield section of the SAF. The local-scale tomography study of Zhang et al. (2009) for a roughly 10 km3 volume centered on SAFOD and the more regional-scale study of Thurber et al. (2006) for a 130 km x 120 km x 20 km volume centered on the 2004 Parkfield earthquake rupture provide what are probably the best 3D images of the seismic velocity structure of the area. The former shows a low velocity zone associated with the SAF extending to significant depth, and both image the well-known velocity contrast across the fault. Seismic tomography generally uses just first P and/or S arrivals because of the relative simplicity of phase picking and ray tracing. Adding secondary arrivals such as FZHW's, however, can enhance the resolution of structure and strengthen constraints on earthquake locations and focal mechanisms. We present a model of 3D velocity structure for the Parkfield region that utilizes a combination of arrival times for FZHW's and the associated direct-wave secondary arrivals as well as existing P-wave arrival time data. The resulting image provides a higher-resolution model of the SAF at depth than previously published models. In addition, we plan to measure polarizations of the direct P and S waves and FZHW's and incorporate the data into our updated velocity tomography/relocation inversion. Through these efforts, we hope to refine the 3D tomographic image of seismic velocity structure and the complex geometry of the active fault strands near SAFOD and along the Parkfield rupture zone.

Seismic imaging of the southern California plate-boundary around the South-Central Transverse Ranges using double-difference tomography

NASA Astrophysics Data System (ADS)

Share, P. E.; Ben-Zion, Y.; Thurber, C. H.; Zhang, H.; Guo, H.

2017-12-01

We derive P and S seismic velocities within and around the South-Central Transverse Ranges section of the San Andreas Fault (SAF), using a new double-difference tomography algorithm incorporating both event-pair and station-pair differential times. The event-pair data can determine high-resolution relative earthquake locations and resolve fine-scale structure in seismogenic zones, whereas station-pair data allow for better absolute locations and higher resolution of structure near the surface where stations are most dense. The tomographic results are based on arrival times of P and S waves generated by 17,753 M>1 local events from 1/1/2010 to 6/30/2015 recorded by 259 stations within a 222 km x 164 km region. The resulting P and S velocity models include low velocities along major fault segments and across-fault velocity contrasts. For example, at depths <7 km, low velocity anomalies delineate the SAF from Cajon Pass to Coachella Valley, with the exception around San Gorgonio Pass (SGP) where a relatively fast rock body cuts across the fault. Extensive faulting and Pelona schist manifest as low velocities throughout the San Bernardino Basin (SBB). High velocity granites abut the SBB to the SW and NE, forming prominent velocity contrasts across the northern San Jacinto Fault Zone (SJFZ) and the SAF, respectively. At depths of 9-11 km, the models also show a velocity contrast with an areal extent of >50 km parallel to the SAF around Coachella Valley but offset to the NE by 13 km. This is interpreted to mark a dipping section of the SAF that separates granites at depth in the SW from gneisses and schists in the NE. Analysis of fault zone head waves propagating along these sections of the SAF and SJFZ show that major bimaterial interfaces are associated with the observed velocity contrasts. Additional features within the models include elongated low velocity anomalies extending from the SJFZ trifurcation area, which itself has associated low velocity at great depth (>14 km), to the Elsinore Fault in the SW. Moreover, a deep (>13 km) velocity contrast appears beneath the SBB with an east-west strike oblique to both the northern SJFZ and SAF traces. The latter is potentially related to the ancestral Banning Fault, which dips to the north, separating low velocity Pelona schist in the north from high velocity granites in the south.

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

NASA Astrophysics Data System (ADS)

Qin, Yanfang; Singh, Satish C.

2017-04-01

The nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Here we present results from seismic full waveform inversion of 12 km long offset seismic reflection data within the trench in the 2004 Sumatra earthquake rupture zone area that provide detailed quantitative information on the incoming oceanic sediments and the trench-fill sediments. The thickness of sediments in this area is 3-4 km, and P wave velocity is as much as 4.5 km/s just above the oceanic crust, suggesting the presence of silica-rich highly compacted and lithified sediments leading to a strong coupling up to the subduction front. We also find an 70-80 m thick low-velocity layer, capped by a high-velocity layer, at 0.8 km above the subducting plate. This low-velocity layer, previously identified as high-amplitude negative polarity reflection, could have porosity of up to 30% containing overpressured fluids, which could act as a protodécollement seaward from the accretionary prism and décollement beneath the forearc. This weak protodécollement combined with the high-velocity indurated sediments above the basement possibly facilitated the rupture propagating up to the front during the 2004 earthquake and enhancing the tsunami. We also find another low-velocity layer within the sediments that may act as a secondary décollement observed offshore central Sumatra, forming bivergent pop-up structures and acting as a conveyer belt in preserving these pop-up structures in the forearc region.

The strong ground motion in Mexico City: array and borehole data analysis.

NASA Astrophysics Data System (ADS)

Roullé, A.; Chávez-García, F. J.

2003-04-01

Site response at Mexico City has been intensively studied for the last 15 years, since the disastrous 1985 earthquakes. After those events, more than 100 accelerographs were installed, and their data have been extremely useful in quantifying amplification and in the subsequent upgrading of the building code. However, detailed analysis of the wavefield has been hampered by the lack of absolute time in the records and the large spacing between stations in terms of dominant wavelengths. In 2001, thanks to the support of CONACYT, Mexico, a new dense accelerographic network was installed in the lake bed zone of Mexico City. The entire network, including an existing network of 3 surface and 2 borehole stations operated by CENAPRED, consists in 12 surface and 4 borehole stations (at 30, 102 and 50 meters). Each station has a 18 bits recorder and a GPS receiver so that the complete network is a 3D array with absolute time. The main objective of this array is to provide data that can help us to better understand the wavefield that propagates in Mexico City during large earthquakes. Last year, a small event of magnitude 6.0 was partially recorded by 6 of the 12 surface stations and all the borehole stations. We analysed the surface data using different array processing techniques such as f-k methods and MUSIC algorithm and the borehole ones using a cross-correlation method. For periods inferior to the site resonance period, the soft clay layer with very low propagation velocities (less than 500 m/s) and a possible multipathing rule the wavefield pattern. For the large period range, the dominant surface wave comes from the epicentral direction and propagates with a quicker velocity (more than 1500 m/s) that corresponds to the velocity of deep layers. The analysis of borehole data shows the presence of different quick wavetrains in the short period range that could correspond to the first harmonic modes of Rayleigh waves. To complete this study, four others events recorded in 1994 by a temporal dense network installed in the firm rock zone of Mexico City were analysed using the same techniques. The results confirm the presence of a diffracting zone south of the valley. These results confirm the hypothesis of a possible interaction between the soft clay layers resonance and diffracted wavetrains of Rayleigh waves to explain both the amplification and the long duration of strong ground motion in Mexico City.

A numerical and experimental investigation on seismic anisotropy of Finero Peridotite, Ivrea-Verbano Zone, northern Italy

NASA Astrophysics Data System (ADS)

Zhong, Xin; Frehner, Marcel; Zappone, Alba; Kunze, Karsten

2014-05-01

We present a combined experimental and numerical study on Finero Peridotite to investigate the major factors creating its seismic anisotropy. We extrapolate the ultrasonic seismic wave velocity measured in a hydrostatic pressure vessel to 0 MPa and 250 MPa confining pressure to compare with numerical simulations at atmospheric pressure and to restore the velocity at in-situ lower crustal conditions, respectively. A linear relation between confining pressure and seismic velocity above 80 MPa reveals the intrinsic mechanical property of the bulk rock without the interference of cracks. To visualize the crystallographic preferred orientation (CPO) we use the electron backscatter diffraction (EBSD) method and create crystallographic orientation maps and pole figures. The first also reveals the shape preferred orientation (SPO). We found that very weak CPO but significant SPO exist in most of the peridotite. The Voigt and Reuss bounds as well as the Hill average (VRH) are calculated from EBSD data to visualize seismic velocity and to calculate anisotropy in the form of velocity pole figures. We perform finite element (FE) simulations of wave propagation on the EBSD crystallographic orientation maps to calculate the effective wave velocity at different propagation angles, hence estimate the anisotropy numerically. In fracture-free models the FE simulation results agree well with the Hill average. In one case of a sample containing fractures the FE simulation yields similar minimal velocity as the laboratory measurement, which lies outside the VR bounds. This is a warning that care has to be taken when using VRH averages in fractured rocks. All three velocity estimates (hydrostatic pressure vessel, VRH average, and FE simulation) result in equally weak seismic anisotropy. This is mainly the consequence of weak CPO. Although SPO is significantly stronger it has minor influence on anisotropy. Hydrous minerals influence the seismic anisotropy only when their modal composition is large enough to allow waves to propagate preferentially through them. Unlike hornblende, phlogopite is not proven to be a major source for the seismic anisotropy due to its small modal composition. Seismic velocity is also influenced by the source frequency distribution. A lower-frequency source in the FE simulations results in lower effective velocity regardless of sample orientation. The frequency spectrum of the propagating wave is modified from source to receiver due to scattering at the mineral grains, thus leading to effective negative attenuation factors peaked at around 1-3 MHz depending on the source spectrum. However, compared with other factors, such as CPO, SPO, fractures, or hydrous mineral phases, the effect of the source frequency distribution is minor, but may be influential when extrapolated to seismic frequencies (Hz-kHz). This study provides a comprehensive method combining laboratory measurements, EBSD data, and numerical simulations to estimate seismic anisotropy. Future work may focus on modeling the influence of different pore fluids or more complex fracture geometries on seismic velocity and anisotropy. Acknowledgements This work was supported by the Swiss National Science Foundation (project UPseis, 200021_143319).

Experimental and Numerical Investigation of Internal Gravity Waves Excited by Turbulent Penetrative Convection in Water Around Its Density Maximum

NASA Astrophysics Data System (ADS)

Perrard, Stéphane; Le Bars, Michaël; Le Gal, Patrice

This study is devoted to the experimental and numerical analysis of the excitation of gravity waves by turbulent convection. This situation is representative of many geophysical or astrophysical systems such as the convective bottom layer of the atmosphere that radiates internal waves in the stratosphere, or the interaction between the convective and the radiative zones in stars. In our experiments, we use water as a working fluid as it possesses the remarkable property of having a maximum density at 4 °C. Therefore, when establishing on a water layer a temperature gradient between 0 °C at the bottom and room temperature at the top, a turbulent convective region appears spontaneously under a stably stratified zone. In these conditions, gravity waves are excited by the convective fluid motions penetrating the stratified layer. Although this type of flow, called penetrative convection, has already been described, we present here the first velocity field measurement of wave emission and propagation. We show in particular that an intermediate layer that we call the buffer layer emerges between the convective and the stratified zones. In this buffer layer, the angle of propagation of the waves varies with the altitude since it is slaved to the Brunt-Väisälä frequency which evolves rapidly between the convective and the stratified layer. A minimum angle is reached at the end of the buffer layer. Then we observe that an angle of propagation is selected when the waves travel through the stratified layer. We expect this process of wave selection to take place in natural situations.

Etude comparative sur la propagation de l'endommagement apres impact des composites carbone/epoxy renforces par piquage au fil Kevlar et titane-nickel

NASA Astrophysics Data System (ADS)

Vachon, Pierre-Luc

Composite laminates have strong in-plane mechanical properties, but they are generally weaker through their thickness. This specificity makes the laminates prone to delamination, particularly under low-velocity impact loads. Consequently numerous research efforts have been dedicated to developing interlaminar reinforcing methods, such as transverse stitching. The present project proposes the use of the stitching technique combined with a special stitching thread made of superelastic TiNi alloy. This technology is intended to improve the delamination toughness in composite laminates loaded in bending. In the first part of this study a numerical model was developed for analyzing composite structures. The 3-D finite element model was built with the ANSYS commercial software using 20-node solid and 8-node shell elements. The progressive damage modeling technique was used, allowing the prediction of delamination propagation in a laminate submitted to various loading modes. The model was validated for a plate under quasi-static traction load, and it was then used to simulate three-point bending tests. Secondly, carbon/epoxy composite panels were fabricated, with each panel containing unstitched and stitched specimens. Two different materials were used for the stitching thread: superelastic TiNi wires and Kevlar threads as a reference. Some stitched specimens were cut in slices in order to make some observations of the internal stitch using an optical microscope. Standardized low-velocity impact tests and compression after impact tests were carried out on stitched and unstitched specimens (ASTM D7136 and D7137). The Kevlar reinforcements have shown great performance in reducing the delaminated zone after impact, as well as in improving the residual compression strength. The TiNi reinforcements provided encouraging results during the impact tests, though being less effective than the Kevlar threads. During the compression after impact tests, only a slight difference could be measured between the TiNi-stitched and the unstitched specimens. Then the bending performance of the specimens was quantified experimentally by calculating the energy required to create a unit volume of damaged material (Gv, J/mm3). This metric is similar to the Strain Energy Release Rate (SERR) commonly used in studies on delamination. According to the experimental results, the damage resistance in three-point bending was not improved by the Kevlar reinforcements, despite the reduced damaged zone after the impact test. Indeed, when the strain energy in bending is relativized to the induced damaged volume during propagation, it turns out that the TiNi reinforcements are more effective than the Kevlar's for improving the damage resistance. Finally, the numerical study on the behavior of both types of stitched reinforcements allowed identifying subtle differences between those. Indeed, both stitching threads (TiNi and Kevlar) promoted the interlaminar propagation of the delamination during simulation of the bending test, with this behavior being less pronounced for the TiNi-stitched plate. However the Kevlar threads seemed more effective for stopping this propagation in the zones between the stitches. Keywords: composite materials, stitching, numerical model, shape memory alloy, three-point bending, low-velocity impact, ultrasound imaging.

Toward a physics-based rate and state friction law for earthquake nucleation processes in fault zones with granular gouge

NASA Astrophysics Data System (ADS)

Ferdowsi, B.; Rubin, A. M.

2017-12-01

Numerical simulations of earthquake nucleation rely on constitutive rate and state evolution laws to model earthquake initiation and propagation processes. The response of different state evolution laws to large velocity increases is an important feature of these constitutive relations that can significantly change the style of earthquake nucleation in numerical models. However, currently there is not a rigorous understanding of the physical origins of the response of bare rock or gouge-filled fault zones to large velocity increases. This in turn hinders our ability to design physics-based friction laws that can appropriately describe those responses. We here argue that most fault zones form a granular gouge after an initial shearing phase and that it is the behavior of the gouge layer that controls the fault friction. We perform numerical experiments of a confined sheared granular gouge under a range of confining stresses and driving velocities relevant to fault zones and apply 1-3 order of magnitude velocity steps to explore dynamical behavior of the system from grain- to macro-scales. We compare our numerical observations with experimental data from biaxial double-direct-shear fault gouge experiments under equivalent loading and driving conditions. Our intention is to first investigate the degree to which these numerical experiments, with Hertzian normal and Coulomb friction laws at the grain-grain contact scale and without any time-dependent plasticity, can reproduce experimental fault gouge behavior. We next compare the behavior observed in numerical experiments with predictions of the Dieterich (Aging) and Ruina (Slip) friction laws. Finally, the numerical observations at the grain and meso-scales will be used for designing a rate and state evolution law that takes into account recent advances in rheology of granular systems, including local and non-local effects, for a wide range of shear rates and slow and fast deformation regimes of the fault gouge.

The effect of compliant prisms on subduction zone earthquakes and tsunamis

NASA Astrophysics Data System (ADS)

Lotto, Gabriel C.; Dunham, Eric M.; Jeppson, Tamara N.; Tobin, Harold J.

2017-01-01

Earthquakes generate tsunamis by coseismically deforming the seafloor, and that deformation is largely controlled by the shallow rupture process. Therefore, in order to better understand how earthquakes generate tsunamis, one must consider the material structure and frictional properties of the shallowest part of the subduction zone, where ruptures often encounter compliant sedimentary prisms. Compliant prisms have been associated with enhanced shallow slip, seafloor deformation, and tsunami heights, particularly in the context of tsunami earthquakes. To rigorously quantify the role compliant prisms play in generating tsunamis, we perform a series of numerical simulations that directly couple dynamic rupture on a dipping thrust fault to the elastodynamic response of the Earth and the acoustic response of the ocean. Gravity is included in our simulations in the context of a linearized Eulerian description of the ocean, which allows us to model tsunami generation and propagation, including dispersion and related nonhydrostatic effects. Our simulations span a three-dimensional parameter space of prism size, prism compliance, and sub-prism friction - specifically, the rate-and-state parameter b - a that determines velocity-weakening or velocity-strengthening behavior. We find that compliant prisms generally slow rupture velocity and, for larger prisms, generate tsunamis more efficiently than subduction zones without prisms. In most but not all cases, larger, more compliant prisms cause greater amounts of shallow slip and larger tsunamis. Furthermore, shallow friction is also quite important in determining overall slip; increasing sub-prism b - a enhances slip everywhere along the fault. Counterintuitively, we find that in simulations with large prisms and velocity-strengthening friction at the base of the prism, increasing prism compliance reduces rather than enhances shallow slip and tsunami wave height.

Dynamic Rupture along a Material Interface: Background, Implications, and Recent Seismological Observations

NASA Astrophysics Data System (ADS)

Ben-Zion, Y.; McGuire, J.

2003-04-01

Natural fault systems have interfaces that separate different media. There are fundamental differences between in-plane ruptures on planar faults that separate similar and dissimilar elastic solids. In a linear isotropic homogeneous solid, slip does not change the normal stress on the rupture plane. However, if the fault separates different materials in-plane slip can produce strong variations of normal stress on the fault. The interaction between slip and normal stress along a material interface can reduce dynamically the frictional strength, making material interfaces mechanically favored surfaces for rupture propagation. Analytical and numerical works (Weertman, 1980; Adams, 1995; Andrews and Ben-Zion, 1997; Ben-Zion and Andrews, 1998) have shown that rupture along a material interface occurs as a narrow wrinkle-like pulse propagating spontaneously only in one direction, that of slip in the more compliant medium. Characteristic features of the wrinkle-like pulse include: (1) Strong correlation between variations of normal stress and slip. (2) Asymmetric motion on different sides of the fault. (3) Preferred direction of rupture propagation. (4) Self-sharpening and divergent behavior with propagation distance. These characteristics can be important to a number of fundamental issues, including trapping of rupture in structures with material interfaces, the heat flow paradox, short rise-time of earthquake slip, possible existence of tensile component of rupture, and spatial distribution of seismic shaking. Rubin and Gillard (2000), Rubin (2002) and McGuire et al. (2002) presented some seismological evidence that rupture propagation along the San Andreas and other large faults is predominantly unidirectional. Features (1)-(4) are consistent with observations from lab sliding and fracture experiments (Anooshehpoor and Brune, 1999; Schallamach, 1971; Samudrala and Rosakis, 2000). Cochard and Rice (2000) performed calculations of rupture along a material interface governed by a regularized friction having a gradual response of strength to an abrupt variation of normal stress. Their calculations confirmed features (1)-(3) and showed hints of feature (4). The latter was not fully developed in their results because the calculations did not extend long enough in time. Ben-Zion and Huang (2002) simulated dynamic rupture on an interface governed by the regularized friction between a low velocity layer and a surrounding host rock. The results show that the self-sharpening and divergent behavior exists also with the regularized friction for large enough propagation distance. The simulations of Ben-Zion and Huang suggest that in fault structures having a low velocity layer, rupture initiated by failing of an asperity with size not larger than the layer width can become a self-sustaining wrinkle-like pulse. However, if the initial asperity is much larger than the layer width, the rupture will not propagate as a self-sustaining pulse (unless there is also an overall contrast across the fault). The Bear Valley section of the San Andreas Fault separates high velocity block on the SW from a low-velocity material on the NE. This contrast is expected to generate a preference for rupture to the SE and fault zone head-waves on the NE block. Using seismograms from a high density temporary array (Thurber et al., 1997), we measured differential travel-times of head-waves along with the geometrical distribution of the stations at which they arrive prior to the direct P-wave. The travel-time data and spatial distribution of events and stations associated with headwave first arrivals are compatible with the theoretical results of Ben-Zion (1989). We are now modeling waveforms to obtain high resolution image of the fault-zone structure. To test the prediction of unidirectional rupture propagation, we estimate the space-time variances of the moment-release distribution of magnitude 2.5-3.0 events using a variation of the Empirical Green's Function technique. Initial results for a few small events indicate rupture propagation in both directions. We are developing a catalog that will hopefully be large enough to provide clear results on this issue.

Ground Motion in Central Mexico: A Comprehensive Analysis

NASA Astrophysics Data System (ADS)

Ramirez-Guzman, L.; Juarez, A.; Rábade, S.; Aguirre, J.; Bielak, J.

2015-12-01

This study presents a detailed analysis of the ground motion in Central Mexico based on numerical simulations, as well as broadband and strong ground motion records. We describe and evaluate a velocity model for Central Mexico derived from noise and regional earthquake cross-correlations, which is used throughout this research to estimate the ground motion in the region. The 3D crustal model includes a geotechnical structure of the Valley of Mexico (VM), subduction zone geometry, and 3D velocity distributions. The latter are based on more than 200 low magnitude (Mw < 4.5) earthquakes and two years of noise recordings. We emphasize the analysis on the ground motion in the Valley of Mexico originating from intra-slab deep events and temblors located along the Pacific coast. Also, we quantify the effects Trans-Mexican Volcanic Belt (TMVB) and the low-velocity deposits on the ground motion. The 3D octree-based finite element wave propagation computations, valid up to 1 Hz, reveal that the inclusion of a basin with a structure as complex as the Valley of Mexico dramatically enhances the regional effects induced by the TMVB. Moreover, the basin not only produces ground motion amplification and anomalous duration, but it also favors the energy focusing into zones of Mexico City where structures typically undergo high levels of damage.

Linking Microearthquakes and Seismic Tomography on the Endeavour Segment of the Juan de Fuca Ridge: Implications for Hydrothermal Circulation

NASA Astrophysics Data System (ADS)

Wilcock, W. S.; Weekly, R. T.; Hooft, E. E.; Toomey, D. R.; Kim, E.

2013-12-01

We report on a remarkable correlation between the patterns of microearthquakes and three-dimensional upper crustal velocity anomalies on the Endeavour segment of the Juan de Fuca Ridge. Microearthquakes were monitored from 2003-2006 by a small seismic network deployed on the central part of the segment. The velocity model was obtained from a tomography experiment comprising over 5500 shots from a large airgun array that were recorded by ocean bottom seismometers deployed at 64 sites along the Endeavour segment and the adjacent overlapping spreading centers (OSCs). On the segment scale, upper crustal velocities are low in the OSCs indicating that the crust is highly fractured. These low velocities persist off-axis and record the history of ridge propagation. In 2005, two swarm sequences that were interpreted in terms of magmatic intrusions on the limbs of the Endeavour-West Valley OSC were accompanied by extensive seismicity within the overlap basin. Throughout the microearthquake experiment earthquakes were concentrated in a region surrounding the southern tip of the West Valley propagator that coincides closely with the southern limit of the low velocities imaged around the OSC. Beneath the hydrothermal vent fields in the center of the Endeavour segment, the earthquakes were mostly located in a 500-m-thick band immediately above the axial magma chamber. There was a close correlation between the rates of seismicity beneath each vent field and their thermal output. The highest rates of seismicity were observed beneath the High Rise and Main Endeavour fields that each have power outputs of several hundred megawatts. Seismic velocities are generally high beneath the vent fields relative to velocities along the ridge axis immediately to the north and south. However, the High Rise and Main Endeavour fields are underlain by a low velocity region at 2 km depth that coincides with the seismically active region. This is consistent with a region of increased fracturing and possibly elevated temperatures in the heat uptake zone. Along the central Endeavour, the levels of seismic anisotropy in the upper crust are high on-axis (~12% at the seafloor decreasing to 5% at 2 km depth) and decrease off-axis by about 50% on a length scale of 5-8 km (0.2-0.3 Myr). This decrease in anisotropy off-axis is accompanied by a 0.2-0.3 km/s increase in isotropic velocities. These observations lead us to infer that in regions where ridge spreading is associated with a narrow zone of deformation overlying an axial magma chamber, the fractures created by spreading processes are rapidly sealed by the mineral alteration and precipitation that accompanies high temperature hydrothermal circulation. Vigorous high-temperature hydrothermal circulation can only persist if there is an ongoing mechanism to form new fractures. In contrast, in OSCs where spreading is associated with a broad zone of deformation, the fractures are preserved off-axis. This suggests that the crust formed at OSCs is more permeable at depth and thus may support deeper and more extensive low-temperature passive hydrothermal circulation than the crust formed elsewhere.

Should tsunami simulations include a nonzero initial horizontal velocity?

NASA Astrophysics Data System (ADS)

Lotto, Gabriel C.; Nava, Gabriel; Dunham, Eric M.

2017-08-01

Tsunami propagation in the open ocean is most commonly modeled by solving the shallow water wave equations. These equations require initial conditions on sea surface height and depth-averaged horizontal particle velocity or, equivalently, horizontal momentum. While most modelers assume that initial velocity is zero, Y.T. Song and collaborators have argued for nonzero initial velocity, claiming that horizontal displacement of a sloping seafloor imparts significant horizontal momentum to the ocean. They show examples in which this effect increases the resulting tsunami height by a factor of two or more relative to models in which initial velocity is zero. We test this claim with a "full-physics" integrated dynamic rupture and tsunami model that couples the elastic response of the Earth to the linearized acoustic-gravitational response of a compressible ocean with gravity; the model self-consistently accounts for seismic waves in the solid Earth, acoustic waves in the ocean, and tsunamis (with dispersion at short wavelengths). Full-physics simulations of subduction zone megathrust ruptures and tsunamis in geometries with a sloping seafloor confirm that substantial horizontal momentum is imparted to the ocean. However, almost all of that initial momentum is carried away by ocean acoustic waves, with negligible momentum imparted to the tsunami. We also compare tsunami propagation in each simulation to that predicted by an equivalent shallow water wave simulation with varying assumptions regarding initial velocity. We find that the initial horizontal velocity conditions proposed by Song and collaborators consistently overestimate the tsunami amplitude and predict an inconsistent wave profile. Finally, we determine tsunami initial conditions that are rigorously consistent with our full-physics simulations by isolating the tsunami waves from ocean acoustic and seismic waves at some final time, and backpropagating the tsunami waves to their initial state by solving the adjoint problem. The resulting initial conditions have negligible horizontal velocity.[Figure not available: see fulltext.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parra, J.; Collier, H.; Angstman, B.

In low porosity, low permeability zones, natural fractures are the primary source of permeability which affect both production and injection of fluids. The open fractures do not contribute much to porosity, but they provide an increased drainage network to any porosity. An important approach to characterizing the fracture orientation and fracture permeability of reservoir formations is one based upon the effects of such conditions on the propagation of acoustic and seismic waves in the rock. We present the feasibility of using seismic measurement techniques to map the fracture zones between wells spaced 2400 ft at depths of about 1000 ft.more » For this purpose we constructed computer models (which include azimuthal anisotropy) using Lodgepole reservoir parameters to predict seismic signatures recorded at the borehole scale, crosswell scale, and 3 D seismic scale. We have integrated well logs with existing 2D surfaces seismic to produce petrophysical and geological cross sections to determine the reservoir parameters and geometry for the computer models. In particular, the model responses are used to evaluate if surface seismic and crosswell seismic measurements can capture the anisotropy due to vertical fractures. Preliminary results suggested that seismic waves transmitted between two wells will propagate in carbonate fracture reservoirs, and the signal can be received above the noise level at the distance of 2400 ft. In addition, the large velocities contrast between the main fracture zone and the underlying unfractured Boundary Ridge Member, suggested that borehole reflection imaging may be appropriate to map and fracture zone thickness variation and fracture distributions in the reservoir.« less

Slip complexity and frictional heterogeneities in dynamic fault models

NASA Astrophysics Data System (ADS)

Bizzarri, A.

2005-12-01

The numerical modeling of earthquake rupture requires the specification of the fault system geometry, the mechanical properties of the media surrounding the fault, the initial conditions and the constitutive law for fault friction. The latter accounts for the fault zone properties and allows for the description of processes of nucleation, propagation, healing and arrest of a spontaneous rupture. In this work I solve the fundamental elasto-dynamic equation for a planar fault, adopting different constitutive equations (slip-dependent and rate- and state-dependent friction laws). We show that the slip patterns may be complicated by different causes. The spatial heterogeneities of constitutive parameters are able to cause the healing of slip, like barrier-healing or slip pulses. Our numerical experiments show that the heterogeneities of the parameter L affect the dynamic rupture propagation and weakly modify the dynamic stress drop and the rupture velocity. The heterogeneity of a and b parameters affects the dynamic rupture propagation in a more complex way: a velocity strengthening area (a > b) can arrest a dynamic rupture, but can be driven to an instability if suddenly loaded by the dynamic rupture front. Our simulations provide a picture of the complex interactions between fault patches having different frictional properties. Moreover, the slip distribution on the fault plane is complicated considering the effects of the rake rotation during the propagation: depending on the position on the fault plane, the orientation of instantaneous total dynamic traction can change with time with respect to the imposed initial stress direction. These temporal rake rotations depend on the amplitude of the initial stress and on its distribution. They also depend on the curvature and direction of the rupture front with respect to the imposed initial stress direction: this explains why rake rotations are mostly located near the rupture front and within the cohesive zone, where the breakdown processes take places. Finally, the rupture behavior, the fault slip distribution and the traction evolution may be changed and complicated including additional physical phenomena, like thermal pressurization of pore fluid (due to frictional heating). Our results involve interesting implications for slip duration and fracture energy.

The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 2. Observed and Modeled Ice Flow

NASA Technical Reports Server (NTRS)

Colgan, William Terence; Rajaram, Harihar; Anderson, Robert S.; Steffen, Konrad; Zwally, H. Jay; Phillips, Thomas; Abdalati, Waleed

2012-01-01

Ice velocities observed in 2005/06 at three GPS stations along the Sermeq Avannarleq flowline, West Greenland, are used to characterize an observed annual velocity cycle. We attempt to reproduce this annual ice velocity cycle using a 1-D ice-flow model with longitudinal stresses coupled to a 1-D hydrology model that governs an empirical basal sliding rule. Seasonal basal sliding velocity is parameterized as a perturbation of prescribed winter sliding velocity that is proportional to the rate of change of glacier water storage. The coupled model reproduces the broad features of the annual basal sliding cycle observed along this flowline, namely a summer speed-up event followed by a fall slowdown event. We also evaluate the hypothesis that the observed annual velocity cycle is due to the annual calving cycle at the terminus. We demonstrate that the ice acceleration due to a catastrophic calving event takes an order of magnitude longer to reach CU/ETH ('Swiss') Camp (46km upstream of the terminus) than is observed. The seasonal acceleration observed at Swiss Camp is therefore unlikely to be the result of velocity perturbations propagated upstream via longitudinal coupling. Instead we interpret this velocity cycle to reflect the local history of glacier water balance.

Rapid high-amplitude circumferential slow wave propagation during normal gastric pacemaking and dysrhythmias

PubMed Central

O'Grady, Gregory; Du, Peng; Paskaranandavadivel, Nira; Angeli, Timothy R.; Lammers, Wim JEP; Asirvatham, Samuel J.; Windsor, John A.; Farrugia, Gianrico; Pullan, Andrew J.; Cheng, Leo K.

2012-01-01

Background Gastric slow waves propagate aborally as rings of excitation. Circumferential propagation does not normally occur, except at the pacemaker region. We hypothesized that: i) the unexplained high-velocity, high-amplitude activity associated with the pacemaker region is a consequence of circumferential propagation; ii) rapid, high-amplitude circumferential propagation emerges during gastric dysrhythmias; iii) the driving network conductance might switch between ICC-MP and circular ICC-IM during circumferential propagation; iv) extracellular amplitudes and velocities are correlated. Methods An experimental-theoretical study was performed. HR gastric mapping was performed in pigs during normal activation, pacing and dysrhythmia. Activation profiles, velocities and amplitudes were quantified. ICC pathways were theoretically evaluated in a bidomain model. Extracellular potentials were modelled as a function of membrane potentials. Key Results High-velocity, high-amplitude activation was only recorded in the pacemaker region when circumferential conduction occurred. Circumferential propagation accompanied dysrhythmia in 8/8 experiments, was faster than longitudinal propagation (8.9 vs 6.9 mm/s; p=0.004), and of higher amplitude (739 vs 528 μV; p=0.007). Simulations predicted that ICC-MP could be the driving network during longitudinal propagation, whereas during ectopic pacemaking, ICC-IM could outpace and activate ICC-MP in the circumferential axis. Experimental and modeling data demonstrated a linear relationship between velocities and amplitudes (p<0.001). Conclusions & Inferences The high-velocity and high-amplitude profile of the normal pacemaker region is due to localized circumferential propagation. Rapid circumferential propagation also emerges during a range of gastric dysrhythmias, elevating extracellular amplitudes and organizing transverse wavefronts. One possible explanation for these findings is bidirectional coupling between ICC-MP and circular ICC-IM networks. PMID:22709238

3D dynamic rupture simulation and local tomography studies following the 2010 Haiti earthquake

NASA Astrophysics Data System (ADS)

Douilly, Roby

The 2010 M7.0 Haiti earthquake was the first major earthquake in southern Haiti in 250 years. As this event could represent the beginning of a new period of active seismicity in the region, and in consideration of how vulnerable the population is to earthquake damage, it is important to understand the nature of this event and how it has influenced seismic hazards in the region. Most significantly, the 2010 earthquake occurred on the secondary Leogâne thrust fault (two fault segments), not the Enriquillo Fault, the major strike-slip fault in the region, despite it being only a few kilometers away. We first use a finite element model to simulate rupture along the Leogâne fault. We varied friction and background stress to investigate the conditions that best explain observed surface deformations and why the rupture did not to jump to the nearby Enriquillo fault. Our model successfully replicated rupture propagation along the two segments of the Leogâne fault, and indicated that a significant stress increase occurred on the top and to the west of the Enriquillo fault. We also investigated the potential ground shaking level in this region if a rupture similar to the Mw 7.0 2010 Haiti earthquake were to occur on the Enriquillo fault. We used a finite element method and assumptions on regional stress to simulate low frequency dynamic rupture propagation for the segment of the Enriquillo fault closer to the capital. The high-frequency ground motion components were calculated using the specific barrier model, and the hybrid synthetics were obtained by combining the low-frequencies ( 1Hz) from the stochastic simulation using matched filtering at a crossover frequency of 1 Hz. The average horizontal peak ground acceleration, computed at several sites of interest through Port-au-Prince (the capital), has a value of 0.35g. Finally, we investigated the 3D local tomography of this region. We considered 897 high-quality records from the earthquake catalog as recorded by temporary station deployments. We only considered events that had at least 6 P and 6 S arrivals, and an azimuthal gap less then 180 degrees, to simultaneously invert for hypocenters and 3D velocity structure in southern Haiti. We used the program VELEST to define a minimum 1D velocity model, which was then used as a starting model in the computer algorithm SIMULPS14 to produce the 3D tomography. Our results show a pronounced low velocity zone across the Logne fault, which is consistent with the sedimentary basin location from the geologic map. We also observe a southeast low velocity zone, which is consistent with a predefined structure in the morphology. Low velocity structure usually correlates with broad zones of deformation, such as the presence of cracks or faults, or from the presence of fluid in the crust. This work provides information that can be used in future studies focusing on how changes in material properties can affect rupture propagation, which is useful to assess the seismic hazard that Haiti and other regions are facing.

Rapid acceleration leads to rapid weakening in earthquake-like laboratory experiments

USGS Publications Warehouse

Chang, Jefferson C.; Lockner, David A.; Reches, Z.

2012-01-01

After nucleation, a large earthquake propagates as an expanding rupture front along a fault. This front activates countless fault patches that slip by consuming energy stored in Earth’s crust. We simulated the slip of a fault patch by rapidly loading an experimental fault with energy stored in a spinning flywheel. The spontaneous evolution of strength, acceleration, and velocity indicates that our experiments are proxies of fault-patch behavior during earthquakes of moment magnitude (Mw) = 4 to 8. We show that seismically determined earthquake parameters (e.g., displacement, velocity, magnitude, or fracture energy) can be used to estimate the intensity of the energy release during an earthquake. Our experiments further indicate that high acceleration imposed by the earthquake’s rupture front quickens dynamic weakening by intense wear of the fault zone.

Examining Structural Controls on Earthquake Rupture Dynamics Along the San Andreas Fault

NASA Astrophysics Data System (ADS)

McGuire, J. J.; Ben-Zion, Y.

2002-12-01

Recent numerical simulations of dynamic rupture [Andrews and Ben-Zion, 1997; Harris and Day, 1997] have confirmed earlier analytical results [Weertman, 1980; Adams, 1995] that a contrast in elastic properties between the two sides of a fault will generate an interaction between the normal stress and fault slip that is not present in a homogeneous medium. It has been shown that for a range of frictional parameters and initial conditions, this interaction produces a statistical preference for unilateral rupture propagation in the direction of slip of the more compliant medium [Ben-Zion and Andrews, 1998; Cochard and Rice, 2000; Ben-Zion and Huang 2002]. Thus, the directivity of earthquake ruptures on large faults with well-developed material interfaces may be controlled by material contrasts of the rocks within and across the fault zone. One of the largest known velocity contrasts across a major crustal fault occurs along the Bear Valley section of the San Andreas where high velocity materials on the SW side (P-velocity >5 km/s) are juxtaposed with low-velocity material on the NE side (P-velocity <4 km/s) down to a depth of about 4 km with a less dramatic contrast continuing to about 8 km [Thurber et al., 1997]. This boundary is strong enough to generate significant head-waves refracted along it that are recorded as the first arrivals at stations close to the fault on the NE side [McNally and McEvilly, 1977]. Rubin and Gillard [2000] and Rubin [2002] relocated the events in this region using NCSN waveform data and found that more than twice as many immediate aftershocks to small earthquakes occurred to the NW of the mainshock as to the SE, which they interpreted as being consistent with a preferred rupture direction to the SE. Their interpretation that aftershocks to microearthquakes occur preferentially in the direction opposite of rupture propagation has not been directly tested and is inconsistent with observations from moderate [Fletcher and Spudich, 1998] and large earthquakes [Kilb et al., 2000], which show considerable variability and possibly the opposite preference. We are attempting to directly test the prediction of a preference for rupture propagation to the SE on this fault segment by combining travel-time and waveform modeling of fault-zone head waves, high precision earthquake relocations, and rupture directivity studies. Initial results indicate that there is considerable variability along strike in the strength of the across-fault velocity contrast, with maximum values reaching about 25-30%. This spatial variability in the strength of the material property contrast would be expected to produce a spatial variability in earthquake rupture directivity. We are developing a catalog of earthquake rupture directivity estimates for magnitude 2 and larger earthquakes to compare with the variations of the velocity contrast and aftershock asymmetry. Initial results indicate that even in the regions of highest velocity contrast, moderate earthquakes (M=3) can still rupture unilaterally to the NE. Detailed high resolution results from head-wave modeling, rupture directivity studies, and earthquake relocations will be presented.

Macroscopic Asymmetry of Dynamic Rupture on a Bimaterial Interface With Velocity- Weakening Friction

NASA Astrophysics Data System (ADS)

Ampuero, J.; Ben-Zion, Y.

2006-12-01

Large faults typically separate rocks of different elastic properties. In-plane ruptures on bimaterial interfaces have remarkable dynamic properties that may be relevant to many issues of basic and applied science (e.g., Ben-Zion, 2001). In contrast to slip between similar media, slip along a bimaterial interface generates dynamic changes of normal stress that modify the local fault strength (e.g., Weertman, 1980). One important issue is whether rupture on a bimaterial interface evolves toward a unilateral wrinkle-like pulse in the direction of motion of the compliant medium (the "preferred" direction), or whether it propagates as a symmetric bilateral crack. Some field data suggest that bimaterial interfaces in natural fault zones produce macroscopic rupture asymmetry (Dor et al., 2006; Lewis et al., 2005, 2006); however, this is a subject of ongoing debate. Rubin and Ampuero (2006) performed numerical simulations of bimaterial ruptures under pure slip-weakening friction. They found bilateral crack-like ruptures without significant asymmetry of slip. For ruptures that stopped in low stress areas, there was asymmetry in the final stress distribution, induced by a small scale pulse that detaches from the crack when it stops. This may provide a mechanism for the observed asymmetry of microearthquakes on segments of the San Andreas fault (Rubin and Gillard, 2000). In addition, the results included very prominent asymmetry of slip velocities at the opposite rupture fronts. In calculations with slip-weakening friction the strong asymmetry of slip velocities can not manifest itself into macroscopic rupture asymmetry. However, incorporating in the simulations rate-dependent friction may produce larger stress drop in the preferred direction, leading to macroscopically asymmetric rupture (Ben-Zion, 2006). In this work we study the effect of velocity-weakening friction on rupture along a bimaterial interface, using 2D in-plane simulations with a spectral boundary integral method and a rate-and-state dependent friction law with strong velocity dependence. The law contains slip-weakening or velocity-weakening as limit cases, depending on the length scale in the state evolution law. The steady-state friction coefficient is inversely proportional to slip-rate, mimicking the weakening mechanisms thought to operate on natural faults at high velocities. We examine the behavior of ruptures triggered by a slightly overstressed nucleation zone of size larger than a critical size derived by linear stability analysis. We characterize the range of friction parameters and initial stress values for which ruptures behave as cracks or pulses, decaying or sustained, with subshear or super-shear speeds. All sustained ruptures are initially bilateral. In the range where sub-shear pulse-like rupture is observed, the ruptures develop strong macroscopic asymmetry with continuing propagation along the bimaterial interface. This is manifested by significantly larger seismic potency and propagation distance in the preferred direction, similar to what was found by Shi and Ben-Zion (2006) with strong nucleation phases and slip-weakening friction. The stress asymmetry mechanism described by Rubin and Ampuero (2006) remains in our velocity-weakening simulations as a super-imposed small-scale feature.

Sill and Laccolith growth by Inflation and Propagation--just not necessarily at the same time

NASA Astrophysics Data System (ADS)

Currier, R. M.; Marsh, B. D.

2013-12-01

Sill and laccolith growth is achieved by two key mechanisms, inflation (vertical growth) and propagation (radial growth). Of the myriad of models proposed for magmatic intrusion, all are variations on the same theme--some combination of inflation and propagation. Because of the inherent observational limitations in studying actual high-level crustal magma emplacement, there remains a poor consensus on any preferred model. To gain insight we have performed a series of simple experiments using layered gelatin as a viscoelastic crustal analog, and molten wax as magma analog. Wax is injected from the base of the gelatin mold, begins ascent as a dike, and is captured by the overlying, more rigid, layer of gelatin. The use of a solidifying magma analog separates these experiments from other gelatin-based studies. When water is used, a common choice for magma analog, the intrusion propagates in an extremely smooth manner. However, at the tip of any magma filled crack, where thickness is at a minimum, propagation and solidification are in fierce competition. The introduction of solidification reveals that emplacement actually occurs as a series of ensuing pulses--at times propagating and inflating concurrently, and at other times growth is achieved solely through propagation, or solely inflation. Unlike models without solidification, here no single combination of propagation and inflation accounts for growth, but rather, the different styles of emplacement reflect the relative competitiveness of propagation and solidification at that time and location. When propagation is fast relative to solidification, growth is smooth, and propagation and inflation occur simultaneously. When solidification dominates, propagation ceases, and growth by inflation becomes the chief emplacement mechanism. Nevertheless, regardless of the strong effect of solidification, building backpressure and the associated crack stresses can disrupt the chill zone at the sill edge, and bring on rapid propagation of magma in conjunction with overall sill deflation. Because the competitiveness of solidification increases with decreasing propagation velocity, and because propagation velocity of a growing magma body must necessarily decrease with time, these mechanisms are a fundamental feature of any magma body that grows for any extended period. Generally, larger flux rates correlate to larger radii and thinner sills. For classical laccolith formation, flux rate must be slow enough for solidification to curtail propagation at an early stage, effectively limiting radial growth and promoting further growth solely via inflation. The effects of this overall process occurs on multiple scales, and the history of the chilled margins can be clearly seen with a series of essentially ';chatter rinds' marking the staccato process of emplacement.

Against dogma: On superluminal propagation in classical electromagnetism

NASA Astrophysics Data System (ADS)

Weatherall, James Owen

2014-11-01

It is deeply entrenched dogma that relativity theory prohibits superluminal propagation. It is also experimentally well-established that under some circumstances, classical electromagnetic fields propagate through a dielectric medium with superluminal group velocities and superluminal phase velocities. But it is usually claimed that these superluminal velocities do not violate the relativistic prohibition. Here I analyze electromagnetic fields in a dielectric medium within a framework for understanding superluminal propagation recently developed by Geroch (1996, 2011) and elaborated by Earman (2014). I will argue that for some parameter values, electromagnetic fields do propagate superluminally in the Geroch-Earman sense.

Propagation velocities of laser-produced plasmas from copper wire targets and water droplets

NASA Technical Reports Server (NTRS)

Song, Kyo-Dong; Alexander, Dennis R.

1994-01-01

Experiments were performed to determine the plasma propagation velocities resulting from KrF laser irradiation of copper wire target (75 microns diameter) and water droplets (75 microns diameter) at irradiance levels ranging from 25 to 150 GW/sq cm. Plasma propagation velocities were measured using a streak camera system oriented orthogonally to the high-energy laser propagation axis. Plasma velocities were studied as a function of position in the focused beam. Results show that both the shape of the plasma formation and material removal from the copper wire are different and depend on whether the targets are focused or slightly defocused (approximately = 0.5 mm movement in the beam axis). Plasma formation and its position relative to the target is an important factor in determining the practical focal point during high-energy laser interaction with materials. At irradiance of 100 GW/sq cm, the air plasma has two weak-velocity components which propagate toward and away from the incident laser while a strong-velocity component propagates away from the laser beam as a detonation wave. Comparison of the measured breakdown velocities (in the range of 2.22-2.27 x 10(exp 5) m/s) for air and the value calculated by the nonlinear breakdown wave theory at irradiance of 100 GW/sq cm showed a quantitative agreement within approximately 50% while the linear theory and Gaussian pulse theory failed. The detonation wave velocities of plasma generated from water droplets and copper wire targets for different focused cases were measured and analyzed theoretically. The propagation velocities of laser-induced plasma liquid droplets obtained by previous research are compared with current work.

Crustal-Scale Seismic Structure From Trench to Forearc in the Cascadia Subduction Zone

NASA Astrophysics Data System (ADS)

Rathnayaka, Sampath; Gao, Haiying

2017-09-01

The (de)hydration process and the amount of hydrated sediment carried by the downgoing oceanic plate play a key role in the subduction dynamics. A high-resolution shear velocity model from the crust down to the uppermost mantle, extending from trench to forearc, is constructed in the northern Cascadia subduction zone to investigate seismic characteristics related to slab deformation and (de)hydration at the plate boundary. A total of 220 seismic stations are used, including the Cascadia Initiative Amphibious Array and inland broadband and short-period stations. The empirical Green's functions extracted from continuous ambient noise data from 2006 to 2014 provide high-quality Rayleigh wave signals at periods of 4-50 s. We simulate wave propagation using finite difference method to generate station Strain Green's Tensors and synthetic waveforms. The phase delays of Rayleigh waves between the observed and synthetic data are measured at multiple period ranges. We then invert for the velocity perturbations from the reference model and progressively improve the model resolution. Our tomographic imaging shows many regional- and local-scale low-velocity features, which are possibly related to slab (de)hydration from the oceanic plate to the overriding plate. Specifically, we observe (1) NW-SE oriented linear low-velocity features across the trench, indicating hydration of the oceanic plate induced by bending-related faultings; (2) W-E oriented fingerlike low-velocity structures off the continental margins due to dehydration of the Juan de Fuca plate; and (3) seismic lows atop the plate interface beneath the Washington forearc, indicating fluid-rich sediments subducted and overthrusted at the accretionary wedge.

Relation between hardness and ultrasonic velocity on pipeline steel welded joints

NASA Astrophysics Data System (ADS)

Carreón, H.; Barrera, G.; Natividad, C.; Salazar, M.; Contreras, A.

2016-04-01

In general, the ultrasonic techniques have been used to determine the mechanical properties of materials based on their relationship with metallurgical characteristics. In this research work, the relationship between ultrasonic wave velocity, hardness and the microstructure of steel pipeline welded joints is investigated. Measurements of ultrasonic wave velocity were made as a function of the location across the weld. Hardness measurements were performed in an attempt to correlate with ultrasonic response. In addition, the coarse and dendritic grain structure of the weld material is extreme and unpredictably anisotropic. Thus, due to the acoustic anisotropy of the crystal, weld material of studied joints is anisotropic too. Such structure is no longer direction-independent to the ultrasonic wave propagation; therefore, the ultrasonic beam deflects and redirects and the wave front becomes distorted. Thus, the use of conventional ultrasonic testing techniques using fixed beam angles is very limited and the application of conventional ultrasonic phased array techniques becomes desirable. This technique is proposed to assist pipeline operators in estimating the hardness through ultrasonic measures to evaluate the susceptibility to stress sulphide cracking and hydrogen-induced cracking due to hard spots in steel pipeline welded joints in service. Sound wave velocity and hardness measurements have been carried out on a steel welded joint. For each section of the welding, weld bead, fusion zone, heat affected zone and base metal were found to correspond particular values of the ultrasound velocity. These results were correlated with electron microscopy observations of the microstructure and sectorial scan view of welded joints by ultrasonic phased array.

Evaluation of arterial propagation velocity based on the automated analysis of the Pulse Wave Shape

NASA Astrophysics Data System (ADS)

Clara, F. M.; Scandurra, A. G.; Meschino, G. J.; Passoni, L. I.

2011-12-01

This paper proposes the automatic estimation of the arterial propagation velocity from the pulse wave raw records measured in the region of the radial artery. A fully automatic process is proposed to select and analyze typical pulse cycles from the raw data. An adaptive neuro-fuzzy inference system, together with a heuristic search is used to find a functional approximation of the pulse wave. The estimation of the propagation velocity is carried out via the analysis of the functional approximation obtained with the fuzzy model. The analysis of the pulse wave records with the proposed methodology showed small differences compared with the method used so far, based on a strong interaction with the user. To evaluate the proposed methodology, we estimated the propagation velocity in a population of healthy men from a wide range of ages. It has been found in these studies that propagation velocity increases linearly with age and it presents a considerable dispersion of values in healthy individuals. We conclude that this process could be used to evaluate indirectly the propagation velocity of the aorta, which is related to physiological age in healthy individuals and with the expectation of life in cardiovascular patients.

Experimental study on the flame behaviors of premixed methane/air mixture in horizontal rectangular ducts

NASA Astrophysics Data System (ADS)

Chen, Dongliang; Sun, Jinhua; Chen, Sining; Liu, Yi; Chu, Guanquan

2007-01-01

In order to explore the flame propagation characteristics and tulip flame formation mechanism of premixed methane/air mixture in horizontal rectangular ducts, the techniques of Schlieren and high-speed video camera are used to study the flame behaviors of the premixed gases in a closed duct and opened one respectively, and the propagation characteristics in both cases and the formation mechanism of the tulip flame are analyzed. The results show that, the propagation flame in a closed duct is prior to form a tulip flame structure than that in an opened duct, and the tulip flame structure formation in a closed duct is related to the flame propagation velocity decrease. The sharp decrease of the flame propagation velocity is one of the reasons to the tulip flame formation, and the decrease of the flame propagation velocity is due to the decrease of the burned product flow velocity mainly.

Motor unit action potential conduction velocity estimated from surface electromyographic signals using image processing techniques.

PubMed

Soares, Fabiano Araujo; Carvalho, João Luiz Azevedo; Miosso, Cristiano Jacques; de Andrade, Marcelino Monteiro; da Rocha, Adson Ferreira

2015-09-17

In surface electromyography (surface EMG, or S-EMG), conduction velocity (CV) refers to the velocity at which the motor unit action potentials (MUAPs) propagate along the muscle fibers, during contractions. The CV is related to the type and diameter of the muscle fibers, ion concentration, pH, and firing rate of the motor units (MUs). The CV can be used in the evaluation of contractile properties of MUs, and of muscle fatigue. The most popular methods for CV estimation are those based on maximum likelihood estimation (MLE). This work proposes an algorithm for estimating CV from S-EMG signals, using digital image processing techniques. The proposed approach is demonstrated and evaluated, using both simulated and experimentally-acquired multichannel S-EMG signals. We show that the proposed algorithm is as precise and accurate as the MLE method in typical conditions of noise and CV. The proposed method is not susceptible to errors associated with MUAP propagation direction or inadequate initialization parameters, which are common with the MLE algorithm. Image processing -based approaches may be useful in S-EMG analysis to extract different physiological parameters from multichannel S-EMG signals. Other new methods based on image processing could also be developed to help solving other tasks in EMG analysis, such as estimation of the CV for individual MUs, localization and tracking of innervation zones, and study of MU recruitment strategies.

Extended pseudo-screen migration with multiple reference velocities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Lian-Jie; Fehler, M.C.

1997-11-01

The pseudo-screen propagator is a kind of one way wave propagation based on the local Born approximation. The problem of the propagator is that it is difficult to calculate the scattered fields when the velocity perturbation is large; not to mention the accuracy of the propagator. We develop an extended pseudo-screen propagator by introducing different reference velocities in different regions of a medium to ensure the condition of small perturbation. The exploding reflector data for a 2D slice of the SEG/EAEG 3D salt model is generated by a finite difference scheme to test the feasibility of the method. The migrationmore » result demonstrates that the method can handle severe lateral velocity variations and provides high quality images for complex structures.« less

Scientific drilling into the San Andreas Fault Zone - an overview of SAFOD's first five years

USGS Publications Warehouse

Zoback, Mark; Hickman, Stephen; Ellsworth, William; ,

2011-01-01

The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes controlling faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD is located near Parkfield, California and penetrates a section of the fault that is moving due to a combination of repeating microearthquakes and fault creep. Geophysical logs define the San Andreas Fault Zone to be relatively broad (~200 m), containing several discrete zones only 2–3 m wide that exhibit very low P- and S-wave velocities and low resistivity. Two of these zones have progressively deformed the cemented casing at measured depths of 3192 m and 3302 m. Cores from both deforming zones contain a pervasively sheared, cohesionless, foliated fault gouge that coincides with casing deformation and explains the observed extremely low seismic velocities and resistivity. These cores are being now extensively tested in laboratories around the world, and their composition, deformation mechanisms, physical properties, and rheological behavior are studied. Downhole measurements show that within 200 m (maximum) of the active fault trace, the direction of maximum horizontal stress remains at a high angle to the San Andreas Fault, consistent with other measurements. The results from the SAFOD Main Hole, together with the stress state determined in the Pilot Hole, are consistent with a strong crust/weak fault model of the San Andreas. Seismic instrumentation has been deployed to study physics of faulting—earthquake nucleation, propagation, and arrest—in order to test how laboratory-derived concepts scale up to earthquakes occurring in nature.

Open ocean dead zones in the tropical North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Karstensen, J.; Fiedler, B.; Schütte, F.; Brandt, P.; Körtzinger, A.; Fischer, G.; Zantopp, R.; Hahn, J.; Visbeck, M.; Wallace, D.

2015-04-01

Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg-1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg-1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day-1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

Dynamics of ionization processes in high-pressure nitrogen, air, and SF{sub 6} during a subnanosecond breakdown initiated by runaway electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarasenko, V. F., E-mail: vft@loi.hcei.tsc.ru; Beloplotov, D. V.; Lomaev, M. I.

2015-10-15

The dynamics of ionization processes in high-pressure nitrogen, air, and SF{sub 6} during breakdown of a gap with a nonuniform distribution of the electric field by nanosecond high-voltage pulses was studied experimentally. Measurements of the amplitude and temporal characteristics of a diffuse discharge and its radiation with a subnanosecond time resolution have shown that, at any polarity of the electrode with a small curvature radius, breakdown of the gap occurs via two ionization waves, the first of which is initiated by runaway electrons. For a voltage pulse with an ∼500-ps front, UV radiation from different zones of a diffuse dischargemore » is measured with a subnanosecond time resolution. It is shown that the propagation velocity of the first ionization wave increases after its front has passed one-half of the gap, as well as when the pressure in the discharge chamber is reduced and/or when SF{sub 6} is replaced with air or nitrogen. It is found that, at nitrogen pressures of 0.4 and 0.7 MPa and the positive polarity of the high-voltage electrode with a small curvature radius, the ionization wave forms with a larger (∼30 ps) time delay with respect to applying the voltage pulse to the gap than at the negative polarity. The velocity of the second ionization wave propagating from the plane electrode is measured. In a discharge in nitrogen at a pressure of 0.7 MPa, this velocity is found to be ∼10 cm/ns. It is shown that, as the nitrogen pressure increases to 0.7 MPa, the propagation velocity of the front of the first ionization wave at the positive polarity of the electrode with a small curvature radius becomes lower than that at the negative polarity.« less

Coda Wave Interferometry Method Applied in Structural Monitoring to Assess Damage Evolution in Masonry and Concrete Structures

NASA Astrophysics Data System (ADS)

Masera, D.; Bocca, P.; Grazzini, A.

2011-07-01

In this experimental program the main goal is to monitor the damage evolution in masonry and concrete structures by Acoustic Emission (AE) signal analysis applying a well-know seismic method. For this reason the concept of the coda wave interferometry is applied to AE signal recorded during the tests. Acoustic Emission (AE) are very effective non-destructive techniques applied to identify micro and macro-defects and their temporal evolution in several materials. This technique permits to estimate the velocity of ultrasound waves propagation and the amount of energy released during fracture propagation to obtain information on the criticality of the ongoing process. By means of AE monitoring, an experimental analysis on a set of reinforced masonry walls under variable amplitude loading and strengthening reinforced concrete (RC) beams under monotonic static load has been carried out. In the reinforced masonry wall, cyclic fatigue stress has been applied to accelerate the static creep and to forecast the corresponding creep behaviour of masonry under static long-time loading. During the tests, the evaluation of fracture growth is monitored by coda wave interferometry which represents a novel approach in structural monitoring based on AE relative change velocity of coda signal. In general, the sensitivity of coda waves has been used to estimate velocity changes in fault zones, in volcanoes, in a mining environment, and in ultrasound experiments. This method uses multiple scattered waves, which travelled through the material along numerous paths, to infer tiny temporal changes in the wave velocity. The applied method has the potential to be used as a "damage-gauge" for monitoring velocity changes as a sign of damage evolution into masonry and concrete structures.

Velocity distributions in a micromixer measured by NMR imaging.

PubMed

Ahola, Susanna; Telkki, Ville-Veikko; Stapf, Siegfried

2012-04-24

Velocity distributions (so-called propagators) with two-dimensional spatial resolution inside a chemical micromixer were measured by pulsed-field-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR). A surface coil matching the volume of interest was built to enhance the signal-to-noise ratio. This enabled the acquisition of velocity maps with a very high spatial resolution of 29 μm × 39 μm. The measured propagators are compared with theoretical distributions and a good agreement is found. The results show that the propagator data provide much richer information about flow behaviour than conventional NMR velocity imaging and the information is essential for understanding the performance of a micromixer. It reveals, for example, deviations in the shape and size of the channel structures and multicomponent flow velocity distribution of overlapping channels. Propagator data efficiently compensate lost information caused by insufficient 3D resolution in conventional velocity imaging.

Should tsunami models use a nonzero initial condition for horizontal velocity?

NASA Astrophysics Data System (ADS)

Nava, G.; Lotto, G. C.; Dunham, E. M.

2017-12-01

Tsunami propagation in the open ocean is most commonly modeled by solving the shallow water wave equations. These equations require two initial conditions: one on sea surface height and another on depth-averaged horizontal particle velocity or, equivalently, horizontal momentum. While most modelers assume that initial velocity is zero, Y.T. Song and collaborators have argued for nonzero initial velocity, claiming that horizontal displacement of a sloping seafloor imparts significant horizontal momentum to the ocean. They show examples in which this effect increases the resulting tsunami height by a factor of two or more relative to models in which initial velocity is zero. We test this claim with a "full-physics" integrated dynamic rupture and tsunami model that couples the elastic response of the Earth to the linearized acoustic-gravitational response of a compressible ocean with gravity; the model self-consistently accounts for seismic waves in the solid Earth, acoustic waves in the ocean, and tsunamis (with dispersion at short wavelengths). We run several full-physics simulations of subduction zone megathrust ruptures and tsunamis in geometries with a sloping seafloor, using both idealized structures and a more realistic Tohoku structure. Substantial horizontal momentum is imparted to the ocean, but almost all momentum is carried away in the form of ocean acoustic waves. We compare tsunami propagation in each full-physics simulation to that predicted by an equivalent shallow water wave simulation with varying assumptions regarding initial conditions. We find that the initial horizontal velocity conditions proposed by Song and collaborators consistently overestimate the tsunami amplitude and predict an inconsistent wave profile. Finally, we determine tsunami initial conditions that are rigorously consistent with our full-physics simulations by isolating the tsunami waves (from ocean acoustic and seismic waves) at some final time, and backpropagating the tsunami waves to their initial state by solving the adjoint problem. The resulting initial conditions have negligible horizontal velocity.

Estimation of seismic velocity in the subducting crust of the Pacific slab beneath Hokkaido, northern Japan by using guided waves

NASA Astrophysics Data System (ADS)

Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.

2014-12-01

A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.

Modelling Subduction Zone Magmatism Due to Hydraulic Fracture

NASA Astrophysics Data System (ADS)

Lawton, R.; Davies, J. H.

2014-12-01

The aim of this project is to test the hypothesis that subduction zone magmatism involves hydraulic fractures propagating from the oceanic crust to the mantle wedge source region (Davies, 1999). We aim to test this hypothesis by developing a numerical model of the process, and then comparing model outputs with observations. The hypothesis proposes that the water interconnects in the slab following an earthquake. If sufficient pressure develops a hydrofracture occurs. The hydrofracture will expand in the direction of the least compressive stress and propagate in the direction of the most compressive stress, which is out into the wedge. Therefore we can calculate the hydrofracture path and end-point, given the start location on the slab and the propagation distance. We can therefore predict where water is added to the mantle wedge. To take this further we have developed a thermal model of a subduction zone. The model uses a finite difference, marker-in-cell method to solve the heat equation (Gerya, 2010). The velocity field was prescribed using the analytical expression of cornerflow (Batchelor, 1967). The markers contained within the fixed grid are used to track the different compositions and their properties. The subduction zone thermal model was benchmarked (Van Keken, 2008). We used the hydrous melting parameterization of Katz et.al., (2003) to calculate the degree of melting caused by the addition of water to the wedge. We investigate models where the hydrofractures, with properties constrained by estimated water fluxes, have random end points. The model predicts degree of melting, magma productivity, temperature of the melt and water content in the melt for different initial water fluxes. Future models will also include the buoyancy effect of the melt and residue. Batchelor, Cambridge UP, 1967. Davies, Nature, 398: 142-145, 1999. Gerya, Cambridge UP, 2010. Katz, Geochem. Geophys. Geosy, 4(9), 2003 Van Keken et.al. Phys. Earth. Planet. In., 171:187-197, 2008.

Effects of Bounded Fault on Seismic Radiation and Rupture Propagation

NASA Astrophysics Data System (ADS)

Weng, H.; Yang, H.

2016-12-01

It has been suggested that narrow rectangle fault may emit stopping phases that can largely affect seismic radiation and thus rupture propagation, e.g., generation of short-duration pulse-like ruptures. Here we investigate the effects of narrow along-dip rectangle fault (analogously to 2015 Nepal earthquake with 200 km * 40 km) on seismic radiation and rupture propagation through numerical modeling in the framework of the linear slip-weakening friction law. First, we found the critical slip-weakening distance Dc may largely affect the seismic radiation and other source parameters, such as rupture speed, final slip and stress drop. Fixing all other uniform parameters, decreasing Dc could decrease the duration time of slip rate and increase the peak slip rate, thus increase the seismic radiation energy spectrum of slip acceleration. In addition, smaller Dc could lead to larger rupture speed (close to S wave velocity), but smaller stress drop and final slip. The results show that Dc may control the efficiency of far-field radiation. Furthermore, the duration time of slip rate at locations close to boundaries is 1.5 - 4 s less than that in the center of the fault. Such boundary effect is especially remarkable for smaller Dc due to the smaller average duration time of slip rate, which could increase the high-frequency radiation energy and impede low-frequency component near the boundaries from the analysis of energy spectrum of slip acceleration. These results show high frequency energy tends to be radiated near the fault boundaries as long as Dc is small enough. In addition, ruptures are fragile and easy to self-arrest if the width of the seismogenic zone is very narrow. In other words, the sizes of nucleation zone need to be larger to initiate runaway ruptures. Our results show the critical sizes of nucleation zones increase as the widths of seismogenic zones decrease.

Dynamics of continental rift propagation: the end-member modes

NASA Astrophysics Data System (ADS)

Van Wijk, J. W.; Blackman, D. K.

2005-01-01

An important aspect of continental rifting is the progressive variation of deformation style along the rift axis during rift propagation. In regions of rift propagation, specifically transition zones from continental rifting to seafloor spreading, it has been observed that contrasting styles of deformation along the axis of rift propagation are bounded by shear zones. The focus of this numerical modeling study is to look at dynamic processes near the tip of a weak zone in continental lithosphere. More specifically, this study explores how modeled rift behavior depends on the value of rheological parameters of the crust. A three-dimensional finite element model is used to simulate lithosphere deformation in an extensional regime. The chosen approach emphasizes understanding the tectonic forces involved in rift propagation. Dependent on plate strength, two end-member modes are distinguished. The stalled rift phase is characterized by absence of rift propagation for a certain amount of time. Extension beyond the edge of the rift tip is no longer localized but occurs over a very wide zone, which requires a buildup of shear stresses near the rift tip and significant intra-plate deformation. This stage represents a situation in which a rift meets a locked zone. Localized deformation changes to distributed deformation in the locked zone, and the two different deformation styles are balanced by a shear zone oriented perpendicular to the trend. In the alternative rift propagation mode, rift propagation is a continuous process when the initial crust is weak. The extension style does not change significantly along the rift axis and lengthening of the rift zone is not accompanied by a buildup of shear stresses. Model predictions address aspects of previously unexplained rift evolution in the Laptev Sea, and its contrast with the tectonic evolution of, for example, the Gulf of Aden and Woodlark Basin.

Study of the Nankai seismogenic fault using dynamic wave propagation modelling of digital rock from the Nobeoka Fault

NASA Astrophysics Data System (ADS)

Eng, Chandoeun; Ikeda, Tatsunori; Tsuji, Takeshi

2018-10-01

To understand the characteristics of the Nankai seismogenic fault in the plate convergent margin, we calculated the P- and S-wave velocities (VP and VS) of digital rock models constructed from core samples of an ancient plate boundary fault at Nobeoka, Kyushu Island, Japan. We first constructed 3D digital rock models from microcomputed tomography images and identified their heterogeneous textures such as cracks and veins. We replaced the cracks and veins with air, water, quartz, calcite and other materials with different bulk and shear moduli. Using the Rotated Staggered Grid Finite-Difference Method, we performed dynamic wave propagation simulations and quantified the effective VP, VS and the ratio of VP to VS (VP/VS) of the 3D digital rock models with different crack-filling minerals. Our results demonstrate that the water-saturated cracks considerably decreased the seismic velocity and increased VP/VS. The VP/VS of the quartz-filled rock model was lower than that in the water-saturated case and in the calcite-filled rock model. By comparing the elastic properties derived from the digital rock models with the seismic velocities (e.g. VP and VP/VS) around the seismogenic fault estimated from field seismic data, we characterised the evolution process of the deep seismogenic fault. The high VP/VS and low VP observed at the transition from aseismic to coseismic regimes in the Nankai Trough can be explained by open cracks (or fractures), while the low VP/VS and high VP observed at the deeper coseismic fault zone suggests quartz-filled cracks. The quartz-rich fault zone characterised as low VP/VS and high VP in this study could partially relate to the coseismic behaviour as suggested by previous studies, because quartz exhibits slip-weakening behaviour (i.e. unstable coseismic slip).

Active-source 3-D tomography near Nias and Batu Islands, offshore central Sumatra

NASA Astrophysics Data System (ADS)

Karplus, M.; Henstock, T.; McNeill, L. C.; Vermeesch, P. M.; Hall, T. R.; Harmon, N.; Barton, P. J.

2013-12-01

Wide-angle reflection and refraction tomography constrain 3-D lithospheric P-wave velocity structure beneath the central Sumatra subduction zone from Nias Island to Siberut, offshore Indonesia at the southern boundary of the 2005 megathrust earthquake rupture. This area includes the earthquake segment boundary near the Batu Islands where the Investigator Fracture Zone is subducted beneath the Eurasian plate. We report along- and across-strike variations in structure of the downgoing slab and overriding plate. Seismic wide-angle data were collected during cruise SO198-1 in May-June 2008. Air gun shots were recorded by 47 temporary ocean bottom seismometers (OBS) deployed in a roughly 200 km by 190 km area, 10 three-component long-term OBS (with differential pressure gauge), and 52 land stations. First arrival refraction modeling using ray tracing and least squares inversion has yielded a lithospheric P-wave velocity model, best-resolved in the top 25 km. We observe velocities of ~4.5-6 km/s within the accretionary prism, which varies by several km in its depth extent. The forearc basin is underlain by high velocities of ~7-8 km/s as shallow as 8 km depth. This high velocity region is likely older forearc oceanic crust, as seen in Cascadia and near Simeulue, offshore Sumatra. The top of the subducting slab ranges in depth from ~10 km near the trench to ~20 km beneath the prism. The top of the slab dips approximately 4-4.5° towards the NE between the trench and the prism. Earthquake hypocenters show the slab dip steepens significantly NE of the forearc basin. We compare our velocity models with models derived from other regions to the north and south along-strike in the Sumatra Subduction Zone, including the 2004-2005 segment boundary at Simeulue. Multi-channel seismic reflection data show that fault structures and reflectivity change considerably along- and across-strike in the central Sumatra subduction zone. Furthermore, regional earthquake locations indicate rupture segmentation along the plate boundary. The Nias segment in the north ruptured in the 2005 M8.7 earthquake. The weakly-coupled Batu segment experiences sporadic clusters of events near the break in the forearc slope. The offshore forearc west of Siberut is characterized by almost aseismic behavior, reflecting the locked state of the plate interface, which hasn't ruptured since the 1797 M8.6-8.8 earthquake. The subducting Investigator Fracture Zone is believed to act as a barrier for propagation of slip during large ruptures. We compare our velocity model with reflection data and rupture segments to characterize differences in the lower plate, upper plate, and plate boundary properties.

Mediterranean extension and the Africa-Eurasia collision

NASA Astrophysics Data System (ADS)

Jolivet, Laurent; Faccenna, Claudio

2000-12-01

A number of tectonic events occurred contemporaneously in the Mediterranean region and the Middle East 30-25 Myr ago. These events are contemporaneous to or immediately followed a strong reduction of the northward absolute motion of Africa. Geological observations in the Neogene extensional basins of the Mediterranean region reveal that extension started synchronously from west to east 30-25 Myr ago. In the western Mediterranean it started in the Gulf of Lion, Valencia trough, and Alboran Sea as well as between the Maures massif and Corsica between 33 and 27 Ma ago. It then propagated eastward and southward to form to Liguro-Provençal basin and the Tyrrhenian Sea. In the eastern Mediterranean, extension started in the Aegean Sea before the deposition of marine sediments onto the collapsed Hellenides in the Aquitanian and before the cooling of high-temperature metamorphic core complexes between 20 and 25 Ma. Foundering of the inner zones of the Carpathians and extension in the Panonnian basin also started in the late Oligocene-early Miocene. The body of the Afro-Arabian plate first collided with Eurasia in the eastern Mediterranean region progressively from the Eocene to the Oligocene. Extensional tectonics was first recorded in the Gulf of Aden, Afar triple junction, and Red Sea region also in the Oligocene. A general magmatic surge occurred above all African hot spots, especially the Afar one. We explore the possibility that these drastic changes in the stress regime of the Mediterranean region and Middle East and the contemporaneous volcanic event were triggerred by the Africa/Arabia-Eurasia collision, which slowed down the motion of Africa. The present-day Mediterranean Sea was then locked between two collision zones, and the velocity of retreat of the African slab increased and became larger than the velocity of convergence leading to backarc extension. East of the Caucasus and northern Zagros collision zone the Afro-Arabian plate was still pulled by the slab pull force in the Zagros subduction zone, which created extensional stresses in the northeast corner of the Afro-Arabian plate. The Arabian plate was formed by propagation of a crack from the Carlsberg ridge westward toward the weak part of the African lithosphere above the Afar plume.

Propagation Velocity of Solid Earth Tides

NASA Astrophysics Data System (ADS)

Pathak, S.

2017-12-01

One of the significant considerations in most of the geodetic investigations is to take into account the outcome of Solid Earth tides on the location and its consequent impact on the time series of coordinates. In this research work, the propagation velocity resulting from the Solid Earth tides between the Indian stations is computed. Mean daily coordinates for the stations have been computed by applying static precise point positioning technique for a day. The computed coordinates are used as an input for computing the tidal displacements at the stations by Gravity method along three directions at 1-minute interval for 24 hours. Further the baseline distances are computed between four Indian stations. Computation of the propagation velocity for Solid Earth tides can be done by the virtue of study of the concurrent effect of it in-between the stations of identified baseline distance along with the time consumed by the tides for reaching from one station to another. The propagation velocity helps in distinguishing the impact at any station if the consequence at a known station for a specific time-period is known. Thus, with the knowledge of propagation velocity, the spatial and temporal effects of solid earth tides can be estimated with respect to a known station. As theoretically explained, the tides generated are due to the position of celestial bodies rotating about Earth. So the need of study is to observe the correlation of propagation velocity with the rotation speed of the Earth. The propagation velocity of Solid Earth tides comes out to be in the range of 440-470 m/s. This velocity comes out to be in a good agreement with the Earth's rotation speed.

Regional Wave Propagation in Southeastern United States

NASA Astrophysics Data System (ADS)

Jemberie, A. L.; Langston, C. A.

2003-12-01

Broad band seismograms from the April 29, 2003, M4.6 Fort Payne, Alabama earthquake are analyzed to infer mechanisms of crustal wave propagation, crust and upper mantle velocity structure in southeastern United States, and source parameters of the event. In particular, we are interested in producing deterministic models of the distance attenuation of earthquake ground motions through computation of synthetic seismograms. The method first requires constraining the source parameters of an earthquake and then modeling the amplitude and times of broadband arrivals within the waveforms to infer appropriate layered earth models. A first look at seismograms recorded by stations outside the Mississippi Embayment (ME) show clear body phases such P, sP, Pnl, Sn and Lg. The ME signals are qualitatively different from others because they have longer durations and large surface waves. A straightforward interpretation of P wave arrival times shows a typical upper mantle velocity of 8.18 km/s. However, there is evidence of significantly higher P phase velocities at epicentral distances between 400 and 600km, that may be caused by a high velocity upper mantle anomaly; triplication of P-waves is seen in these seismograms. The arrival time differences between regional P and the depth phase sP at different stations are used to constrain the depth of the earthquake. The source depth lies between 9.5 km and 13km which is somewhat more shallow than the network location that was constrained to 15km depth. The Fort Payne earthquake is the largest earthquake to have occurred within the Eastern Tennessee Seismic Zone.

The transition of dynamic rupture styles in elastic media under velocity-weakening friction

NASA Astrophysics Data System (ADS)

Gabriel, A.-A.; Ampuero, J.-P.; Dalguer, L. A.; Mai, P. M.

2012-09-01

Although kinematic earthquake source inversions show dominantly pulse-like subshear rupture behavior, seismological observations, laboratory experiments and theoretical models indicate that earthquakes can operate with different rupture styles: either as pulses or cracks, that propagate at subshear or supershear speeds. The determination of rupture style and speed has important implications for ground motions and may inform about the state of stress and strength of active fault zones. We conduct 2D in-plane dynamic rupture simulations with a spectral element method to investigate the diversity of rupture styles on faults governed by velocity-and-state-dependent friction with dramatic velocity-weakening at high slip rate. Our rupture models are governed by uniform initial stresses, and are artificially initiated. We identify the conditions that lead to different rupture styles by investigating the transitions between decaying, steady state and growing pulses, cracks, sub-shear and super-shear ruptures as a function of background stress, nucleation size and characteristic velocity at the onset of severe weakening. Our models show that small changes of background stress or nucleation size may lead to dramatic changes of rupture style. We characterize the asymptotic properties of steady state and self-similar pulses as a function of background stress. We show that an earthquake may not be restricted to a single rupture style, but that complex rupture patterns may emerge that consist of multiple rupture fronts, possibly involving different styles and back-propagating fronts. We also demonstrate the possibility of a super-shear transition for pulse-like ruptures. Finally, we draw connections between our findings and recent seismological observations.

Effects of the concentration of emulsion of oil-in-water on the propagation velocity and attenuation

NASA Astrophysics Data System (ADS)

Silva, L. S. F.; Bibiano, D. S.; Figueiredo, M. K. K.; Costa-Félix, R. P. B.

2015-01-01

Soybean oil is an important feedstock for production of biodiesel that generates about 20 % of oily effluents. This paper studied the effect of concentration of soybean oil-inwater emulsions, in the range from 6 000 to 14 000 ppm, on the propagation velocity and ultrasonic attenuation. The Emission-Reception method has shown that the propagation velocity depends linearly on the concentration. The behavior of attenuation is similar to the velocity. Thus, both parameters can be used to measure oils and greases content in water.

Slip events propagating along a ductile mid-crustal strike-slip shear zone (Malpica-Lamego line, Variscan Orogen, NW Iberia)

NASA Astrophysics Data System (ADS)

Llana-Fúnez, Sergio; de Paola, Nicola; Pozzi, Giacomo; Lopez-Sanchez, Marco Antonio

2017-04-01

The current level of erosion in NW Iberian peninsula exposes Variscan mid-crustal depths, where widespread deformation during orogenesis produced dominantly ductile structures. It constitutes an adequate window for the observation of structures close to the brittle-plastic transition in the continental crust. The shear zone object of this work is the Malpica-Lamego line (MLL), a major Variscan structure formed in the late stages of the Variscan collision. The MLL is a mostly strike-slip major structure that offsets laterally by several kilometres the assembly of allochthonous complexes, that contain a sub-horizontal suture zone, which are the remnants of the plate duplication during the Variscan convergence. The shear zone is exposed along the northern coast of Galicia (NW Spain). It is characterized by phyllonites and quartz-mylonites in a zone which is tens of meters in thickness. Within the phyllonites, a few seams of cataclastic rocks have been found in bands along the main fabric. Their cohesive character, the parallelism between the different bands, the fact that host rocks maintain mineral assemblage and that no cross-cutting relations in the field were identified, are considered indicative of these brittle structures forming coetaneously with the ductile shearing producing the phyllonites. Samples from the phyllonites, also from quartz-mylonites, were prepared and powdered to characterize friction properties in a rotary shear apparatus at high, seismic velocities (m/s). Preliminary experiments run at room temperature and effective normal stresses between 10 to 25 MPa, show that friction coefficients µ are relatively high and a limited drop in friction coefficient occurs after 10-20 cm of slip, with µ decreasing from 0.7 to 0.5. Fracturing seems coetaneous with dominant ductile shearing within the shear zone, however, given the frictional properties of the phyllonites, it is unlikely that brittle deformation nucleates within these fault rocks. Instead, it seems that faulting originated in other sectors of the fault zone, and then propagated through the studied section.

Crystal plastic earthquakes in dolostones: from slow to fast ruptures.

NASA Astrophysics Data System (ADS)

Passelegue, F. X.; Aubry, J.; Nicolas, A.; Fondriest, M.; Schubnel, A.; Di Toro, G.

2017-12-01

Dolostone is the most dominant lithology of the seismogenic upper crust around the Mediterranean Sea. Understanding the internal mechanisms controlling fault friction is crucial for understanding seismicity along active faults. Displacement in such fault zones is frequently highlighted by highly reflective (mirror-like) slip surfaces, created by thin films of nanogranular fault rock. Using saw-cut dolostone samples coming from natural fault zones, we conducted stick-slip experiments under triaxial loading conditions at 30, 60 and 90 MPa confining pressure and temperature ranging from 30 to 100 degrees C. At 30 and 65 degrees C, only slow rupture was observed and the experimental fault exhibits frictional behaviour, i.e. a dependence of normal stress on peak shear stress. At 65 degrees C, a strengthening behaviour is observed after the main rupture, leading to a succession of slow rupture. At 100 degrees C, the macroscopic behaviour of the fault becomes ductile, and no dependence of pressure on the peak shear stress is observed. In addition, the increase of the confining pressure up to 60 and 90 MPa allow the transition from slow to fast rupture, highlighted by the records of acoustic activity and by dynamic stress drop occurring in a few tens of microseconds. Using strain gages located along the fault surface and acoustic transducers, we were able to measure the rupture velocities during slow and fast rupture. Slow ruptures propagated around 0.1 m/s, in agreement with natural observations. Fast ruptures propagated up to supershear velocities, i.e. faster than the shear wave speed (>3500 m/s). A complete study of the microstructures was realized before and after ruptures. Slow ruptures lead to the production of mirror-like surface driven by the production of nanograins due to dislocation processes. Fast ruptures induce the production of amorphous material along the fault surface, which may come from decarbonation and melting processes. We demonstrate that the transition from slow to fast instabilities is observed due to an increase of the fault stiffness with increasing both temperature and confining pressure. This increase in the stiffness leads to an increase of the slip velocity during the main instability, which allow flash weakening processes and fast propagation of the seismic rupture.

Refracted arrival waves in a zone of silence from a finite thickness mixing layer.

PubMed

Suzuki, Takao; Lele, Sanjiva K

2002-02-01

Refracted arrival waves which propagate in the zone of silence of a finite thickness mixing layer are analyzed using geometrical acoustics in two dimensions. Here, two simplifying assumptions are made: (i) the mean flow field is transversely sheared, and (ii) the mean velocity and temperature profiles approach the free-stream conditions exponentially. Under these assumptions, ray trajectories are analytically solved, and a formula for acoustic pressure amplitude in the far field is derived in the high-frequency limit. This formula is compared with the existing theory based on a vortex sheet corresponding to the low-frequency limit. The analysis covers the dependence on the Mach number as well as on the temperature ratio. The results show that both limits have some qualitative similarities, but the amplitude in the zone of silence at high frequencies is proportional to omega(-1/2), while that at low frequencies is proportional to omega(-3/2), omega being the angular frequency of the source.

Acute effects of ultrafiltration on aortic mechanical properties determined by measurement of pulse wave velocity and pulse propagation time in hemodialysis patients

PubMed Central

Yıldız, Banu Şahin; Şahin, Alparslan; Aladağ, Nazire Başkurt; Arslan, Gülgün; Kaptanoğulları, Hakan; Akın, İbrahim; Yıldız, Mustafa

2015-01-01

Objective: The effects of acute hemodialysis session on pulse wave velocity are conflicting. The aim of the current study was to assess the acute effects of ultrafiltration on the aortic mechanical properties using carotid-femoral (aortic) pulse wave velocity and pulse propagation time. Methods: A total of 26 (12 women, 14 men) consecutive patients on maintenance hemodialysis (mean dialysis duration: 40.7±25.6 (4-70) months) and 29 healthy subjects (13 women, 16 men) were included in this study. Baseline blood pressure, carotid-femoral (aortic) pulse wave velocity, and pulse propagation time were measured using a Complior Colson device (Createch Industrie, France) before and immediately after the end of the dialysis session. Results: While systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and pulse wave velocity were significantly higher in patients on hemodialysis than in healthy subjects, pulse propagation time was significantly higher in healthy subjects. Although body weight, systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and pulse wave velocity were significantly decreased, heart rate and pulse propagation time were significantly increased after ultrafiltration. There was a significant positive correlation between pulse wave velocity and age, body height, waist circumference, systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and heart rate. Conclusion: Although hemodialysis treatment may chronically worsen aortic mechanical properties, ultrafiltration during hemodialysis may significantly improve aortic pulse wave velocity, which is inversely related to aortic distensibility and pulse propagation time. PMID:25413228

Surface streamer propagations on an alumina bead: experimental observation and numerical modeling

NASA Astrophysics Data System (ADS)

Kang, Woo Seok; Kim, Hyun-Ha; Teramoto, Yoshiyuki; Ogata, Atsushi; Lee, Jin Young; Kim, Dae-Woong; Hur, Min; Song, Young-Hoon

2018-01-01

A surface streamer in a simplified packed-bed reactor has been studied both experimentally (through time-resolved ICCD imaging) and theoretically (through two-dimensional numerical modeling). The propagation of streamers on an alumina spherical bead without catalytic coating shows three distinct phases—the generation and propagation of a primary streamer (PS) with a moderate velocity and electric field, fast PS acceleration with an enhanced electric field, and slow secondary streamer (SS) propagation. The velocity of the streamer is less than that of propagation in a gaseous media. The electric field and velocity at the streamer front are maximized when a PS propagates during the interval from the midpoint of the bead to the bottom electrode. The SS exhibits a much lower velocity and electric field compared with the PS. The PS velocity is affected by an external applied voltage, especially when it approaches the ground electrode. However, that of the SS remains constant regardless of the voltage change. The simulation shows that the PS exhibits a high electric field mainly created by the space charge induced by electrons, whereas the SS relies on ion movement with electron decay in a charge-filled thin streamer body.

Physical properties of fault zone rocks from SAFOD: Tying logging data to high-pressure measurements on drill core

NASA Astrophysics Data System (ADS)

Jeppson, T.; Tobin, H. J.

2013-12-01

In the summer of 2005, Phase 2 of the San Andreas Fault Observatory at Depth (SAFOD) borehole was completed and logged with wireline tools including a dipole sonic tool to measure P- and S-wave velocities. A zone of anomalously low velocity was detected from 3150 to 3414 m measured depth (MD), corresponding with the subsurface location of the San Andreas Fault Zone (SAFZ). This low velocity zone is 5-30% slower than the surrounding host rock. Within this broad low-velocity zone, several slip surfaces were identified as well as two actively deforming shear zones: the southwest deformation zone (SDZ) and the central deformation zone (CDZ), located at 3192 and 3302 m MD, respectively. The SAFZ had also previously been identified as a low velocity zone in seismic velocity inversion models. The anomalously low velocity was hypothesized to result from either (a) brittle deformation in the damage zone of the fault, (b) high fluid pressures with in the fault zone, or (c) lithological variation, or a combination of the above. We measured P- and S-wave velocities at ultrasonic frequencies on saturated 2.5 cm diameter core plug samples taken from SAFOD core obtained in 2007 from within the low velocity zone. The resulting values fall into two distinct groups: foliated fault gouge and non-gouge. Samples of the foliated fault gouge have P-wave velocities between 2.3-3.5 km/s while non-gouge samples lie between 4.1-5.4 km/s over a range of effective pressures from 5-70 MPa. There is a good correlation between the log measurements and laboratory values of P-and S wave velocity at in situ pressure conditions especially for the foliated fault gouge. For non-gouge samples the laboratory values are approximately 0.08-0.73 km/s faster than the log values. This difference places the non-gouge velocities within the Great Valley siltstone velocity range, as measured by logs and ultrasonic measurements performed on outcrop samples. As a high fluid pressure zone was not encountered during SAFOD drilling, we use the ultrasonic velocities of SAFOD core and analogous outcrop samples to determine if the velocity reduction is due to lithologic variations or the presence of deformational fabrics and alteration in the fault zone. Preliminary analysis indicates that while the decrease in velocity across the broad fault zone is heavily influenced by fractures, the extremely low velocities associated with the actively deforming zones are more likely caused by the development of scaly fabric with clay coatings on the fracture surfaces. Analysis of thin sections and well logs are used to support this interpretation.

Surface Current Density Mapping for Identification of Gastric Slow Wave Propagation

PubMed Central

Bradshaw, L. A.; Cheng, L. K.; Richards, W. O.; Pullan, A. J.

2009-01-01

The magnetogastrogram records clinically relevant parameters of the electrical slow wave of the stomach noninvasively. Besides slow wave frequency, gastric slow wave propagation velocity is a potentially useful clinical indicator of the state of health of gastric tissue, but it is a difficult parameter to determine from noninvasive bioelectric or biomagnetic measurements. We present a method for computing the surface current density (SCD) from multichannel magnetogastrogram recordings that allows computation of the propagation velocity of the gastric slow wave. A moving dipole source model with hypothetical as well as realistic biomagnetometer parameters demonstrates that while a relatively sparse array of magnetometer sensors is sufficient to compute a single average propagation velocity, more detailed information about spatial variations in propagation velocity requires higher density magnetometer arrays. Finally, the method is validated with simultaneous MGG and serosal EMG measurements in a porcine subject. PMID:19403355

Past seismic slip-to-the-trench recorded in Central America megathrust

NASA Astrophysics Data System (ADS)

Vannucchi, Paola; Spagnuolo, Elena; Aretusini, Stefano; Di Toro, Giulio; Ujiie, Kohtaro; Tsutsumi, Akito; Nielsen, Stefan

2017-12-01

The 2011 Tōhoku-Oki earthquake revealed that co-seismic displacement along the plate boundary megathrust can propagate to the trench. Co-seismic slip to the trench amplifies hazards at subduction zones, so its historical occurrence should also be investigated globally. Here we combine structural and experimental analyses of core samples taken offshore from southeastern Costa Rica as part of the Integrated Ocean Drilling Program (IODP) Expedition 344, with three-dimensional seismic reflection images of the subduction zone. We document a geologic record of past co-seismic slip to the trench. The core passed through a less than 1.9-million-year-old megathrust frontal ramp that superimposes older Miocene biogenic oozes onto late Miocene-Pleistocene silty clays. This, together with our stratigraphic analyses and geophysical images, constrains the position of the basal decollement to lie within the biogenic oozes. Our friction experiments show that, when wet, silty clays and biogenic oozes are both slip-weakening at sub-seismic and seismic slip velocities. Oozes are stronger than silty clays at slip velocities of less than or equal to 0.01 m s-1, and wet oozes become as weak as silty clays only at a slip velocity of 1 m s-1. We therefore suggest that the geological structures found offshore from Costa Rica were deformed during seismic slip-to-the-trench events. During slower aseismic creep, deformation would have preferentially localized within the silty clays.

Effect of a Material Contrast on a Dynamic Rupture: 3-D

NASA Astrophysics Data System (ADS)

Harris, R. A.; Day, S. M.

2003-12-01

We use numerical simulations of spontaneously propagating ruptures to examine the effect of a material contrast on earthquake dynamics. We specifically study the case of a lateral contrast whereby the fault is the boundary between two different rock-types. This scenario was previously studied in two-dimensions by Harris and Day [BSSA, 1997], and Andrews and Ben-Zion [JGR, 1997], in addition to subsequent 2-D studies, but it has not been known if the two-dimensional results are applicable to the real three-dimensional world. The addition of the third dimension implies a transition from pure mode II (i.e., plane-strain) to mixed-mode crack dynamics, which is more complicated since in mode II the shear and normal stresses are coupled whereas in mode III (i.e., anti-plane strain) they are not coupled. We use a slip-weakening fracture criterion and examine the effect on an earthquake rupture of material contrasts of up to 50 percent across the fault zone. We find a surprisingly good agreement between our earlier 2-D results, and our 3-D results for along-strike propagation. We find that the analytical solution presented in Harris and Day [BSSA, 1997] does an excellent job at predicting the bilateral, along-strike rupture velocities for the three-dimensional situation. In contrast, the along-dip propagation behaves much as expected for a purely mode-III rupture, with the rupture velocities up-dip and down-dip showing the expected symmetries.

Velocities of Subducted Sediments and Continents

NASA Astrophysics Data System (ADS)

Hacker, B. R.; van Keken, P. E.; Abers, G. A.; Seward, G.

2009-12-01

The growing capability to measure seismic velocities in subduction zones has led to unusual observations. For example, although most minerals have VP/ VS ratios around 1.77, ratios <1.7 and >1.8 have been observed. Here we explore the velocities of subducted sediments and continental crust from trench to sub-arc depths using two methods. (1) Mineralogy was calculated as a function of P & T for a range of subducted sediment compositions using Perple_X, and rock velocities were calculated using the methodology of Hacker & Abers [2004]. Calculated slab-top temperatures have 3 distinct depth intervals with different dP/dT gradients that are determined by how coupling between the slab and mantle wedge is modeled. These three depth intervals show concomitant changes in VP and VS: velocities initially increase with depth, then decrease beyond the modeled decoupling depth where induced flow in the wedge causes rapid heating, and increase again at depth. Subducted limestones, composed chiefly of aragonite, show monotonic increases in VP/ VS from 1.63 to 1.72. Cherts show large jumps in VP/ VS from 1.55-1.65 to 1.75 associated with the quartz-coesite transition. Terrigenous sediments dominated by quartz and mica show similar, but more-subdued, transitions from ~1.67 to 1.78. Pelagic sediments dominated by mica and clinopyroxene show near-monotonic increases in VP/ VS from 1.74 to 1.80. Subducted continental crust that is too dry to transform to high-pressure minerals has a VP/ VS ratio of 1.68-1.70. (2) Velocity anisotropy calculations were made for the same P-T dependent mineralogies using the Christoffel equation and crystal preferred orientations measured via electron-backscatter diffraction for typical constituent phases. The calculated velocity anisotropies range from 5-30%. For quartz-rich rocks, the calculated velocities show a distinct depth dependence because crystal slip systems and CPOs change with temperature. In such rocks, the fast VP direction varies from slab-normal at shallow depths through trench-parallel at moderate depths to down-dip approaching sub-arc depths. Vertically incident waves have VP/ VS of 1.7-1.3 over the same range of depths, waves propagating up dip have VP/ VS of 1.7-1.3, and waves propagating along the slab at constant depth have VP/ VS of 1.7-1.45. These remarkably low VP/ VS ratios are due to the anomalous elastic behavior of quartz. More aluminous lithologies have elevated VP/ VS ratios: 1.85 for slab-normal waves, 1.75 for trench-parallel waves, and 1.65 for down-dip waves. Subducted continental crust that is too dry to transform to high-pressure minerals has relatively ordinary VP/ VS ratio of 1.71-1.75 for vertically incident waves, 1.6-1.7 for waves propagating up dip, and 1.65-1.75 for waves propagating along the slab. Thus, subducted mica-rich sediments can have high VP/ VS ratios, whereas quartzose lithologies generate low VP/ VS ratios.

Propagation Dynamics Associated with Resonant Magnetic Perturbation Fields in High-Confinement Mode Plasmas inside the KSTAR Tokamak.

PubMed

Xiao, W W; Evans, T E; Tynan, G R; Yoon, S W; Jeon, Y M; Ko, W H; Nam, Y U; Oh, Y K

2017-11-17

The propagation dynamics of resonant magnetic perturbation fields in KSTAR H-mode plasmas with injection of small edge perturbations produced by a supersonic molecular beam injection is reported for the first time. The results show that the perturbation field first excites a plasma response on the q=3 magnetic surface and then propagates inward to the q=2 surface with a radially averaged propagation velocity of resonant magnetic perturbations field equal to 32.5  m/ s. As a result, the perturbation field brakes the toroidal rotation on the q=3 surface first causing a momentum transport perturbation that propagates both inward and outward. A higher density fluctuation level is observed. The propagation velocity of the resonant magnetic perturbations field is larger than the radial propagation velocity of the perturbation in the toroidal rotation.

Propagation velocity and space-time correlation of perturbations in turbulent channel flow

NASA Technical Reports Server (NTRS)

Kim, John; Hussain, Fazle

1992-01-01

A database obtained from direct numerical simulation of a turbulent channel flow is analyzed to extract the propagation velocity V of velocity, vorticity, and pressure fluctuations from their space-time correlations. A surprising result is that V is approximately the same as the local mean velocity for most of the channel, except for the near-wall region. For y(+) is less than or equal to 15, V is virtually constant, implying that perturbations of all flow variables propagate like waves near the wall. In this region V is 55 percent of the centerline velocity U(sub c) for velocity and vorticity perturbations and 75 percent of U(sub c) for pressure perturbations. Scale-dependence of V is also examined by analyzing the bandpass filtered flow fields. Comprehensive documentation of the propagation velocities and space-time correlation data, which should prove useful in the evaluation of Taylor's hypothesis is presented. An attempt was made to explain some of the data in terms of our current understanding of organized structures, although not all of the data can be explained this way.

Distribution of electromagnetic field and group velocities in two-dimensional periodic systems with dissipative metallic components

NASA Astrophysics Data System (ADS)

Kuzmiak, Vladimir; Maradudin, Alexei A.

1998-09-01

We study the distribution of the electromagnetic field of the eigenmodes and corresponding group velocities associated with the photonic band structures of two-dimensional periodic systems consisting of an array of infinitely long parallel metallic rods whose intersections with a perpendicular plane form a simple square lattice. We consider both nondissipative and lossy metallic components characterized by a complex frequency-dependent dielectric function. Our analysis is based on the calculation of the complex photonic band structure obtained by using a modified plane-wave method that transforms the problem of solving Maxwell's equations into the problem of diagonalizing an equivalent non-Hermitian matrix. In order to investigate the nature and the symmetry properties of the eigenvectors, which significantly affect the optical properties of the photonic lattices, we evaluate the associated field distribution at the high symmetry points and along high symmetry directions in the two-dimensional first Brillouin zone of the periodic system. By considering both lossless and lossy metallic rods we study the effect of damping on the spatial distribution of the eigenvectors. Then we use the Hellmann-Feynman theorem and the eigenvectors and eigenfrequencies obtained from a photonic band-structure calculation based on a standard plane-wave approach applied to the nondissipative system to calculate the components of the group velocities associated with individual bands as functions of the wave vector in the first Brillouin zone. From the group velocity of each eigenmode the flow of energy is examined. The results obtained indicate a strong directional dependence of the group velocity, and confirm the experimental observation that a photonic crystal is a potentially efficient tool in controlling photon propagation.

Cross-shore transport of nearshore sediment by river plume frontal pumping

NASA Astrophysics Data System (ADS)

Horner-Devine, Alexander R.; Pietrzak, Julie D.; Souza, Alejandro J.; McKeon, Margaret A.; Meirelles, Saulo; Henriquez, Martijn; Flores, Raúl P.; Rijnsburger, Sabine

2017-06-01

We present a new mechanism for cross-shore transport of fine sediment from the nearshore to the inner shelf resulting from the onshore propagation of river plume fronts. Onshore frontal propagation is observed in moorings and radar images, which show that fronts penetrate onshore through the nearshore and surf zone, almost to the waterline. During frontal passage a two-layer counterrotating velocity field characteristic of tidal straining is immediately set up, generating a net offshore flow beneath the plume. The seaward flow at depth carries with it high suspended sediment concentrations, which appear to have been generated by wave resuspension in the nearshore region. These observations describe a mechanism by which vertical density stratification can drive exchange of material between the nearshore region and the inner shelf. To our knowledge these are the first observations of this frontal pumping mechanism, which is expected to play an important role in sediment transport near river mouths.

The pattern of deep structure and recent tectonics of the Greater Caucasus in the Ossetian sector from the complex geophysical data

NASA Astrophysics Data System (ADS)

Gorbatikov, A. V.; Rogozhin, E. A.; Stepanova, M. Yu.; Kharazova, Yu. V.; Andreeva, N. V.; Perederin, F. V.; Zaalishvili, V. B.; Mel'kov, D. A.; Dzeranov, B. V.; Dzeboev, B. A.; Gabaraev, A. F.

2015-01-01

Microseismic sounding along the profile in the Ossetian sector of the Greater Caucasus revealed two domains with characteristic properties and morphology deep beneath the mountain system. One subvertical domain is marked with low velocities and the other, also subvertical, has high velocities. The high-velocity zone is largely located beneath the northern limb and axial part of the Greater Caucasus mega-anticlinorium, whereas the low velocity zone projects on the southern limb. Almost throughout the entire structure of the block part of the northern limb of mega-anticlinorium, the top of the high-velocity zone beneath it is consistently horizontal at a depth of ˜10 km. This pattern is violated by the apparent steep rise of the top of the high-velocity zone to the surface in the southern direction, which starts approximately from the main thrust. Beneath the southern limb, the top boundary can also be guessed at a depth of ˜10 km, although less reliably. The roots of the low-velocity zone stretch to a depth of ˜50-60 km and narrow with the depth. The weak regional seismicity quite distinctly maps onto the high-velocity zone. In the depth interval of 10 to 25 km, weak seismicity abruptly drops northwards at the transition to the low-velocity zone. The independent magnetotelluric data show that electric resistivity of the low-velocity zone significantly exceeds the resistivity of the hosting rocks. The model of a medium filled with isolated fractures with mineralized fluid is suggested for the low-velocity zone. According to a series of features, the low-velocity zone tends to float up; in particular, there is a high lateral correlation between the most elevated part of the mountain relief, morphology, and age of the rocks, on one hand, and the position of the low-velocity zone, on the other hand.

Consequences of Rift Propagation for Spreading in Thick Oceanic Crust in Iceland

NASA Astrophysics Data System (ADS)

Karson, J. A.

2015-12-01

Iceland has long been considered a natural laboratory for processes related to seafloor spreading, including propagating rifts, migrating transforms and rotating microplates. The thick, hot, weak crust and subaerial processes of Iceland result in variations on the themes developed along more typical parts of the global MOR system. Compared to most other parts of the MOR, Icelandic rift zones and transform faults are wider and more complex. Rift zones are defined by overlapping arrays of volcanic/tectonic spreading segments as much as 50 km wide. The most active rift zones propagate N and S away from the Iceland hot spot causing migration of transform faults. A trail of crust deformed by bookshelf faulting forms in their wakes. Dead or dying transform strands are truncated along pseudofaults that define propagation rates close to the full spreading rate of ~20 mm/yr. Pseudofaults are blurred by spreading across wide rift zones and laterally extensive subaerial lava flows. Propagation, with decreasing spreading toward the propagator tips causes rotation of crustal blocks on both sides of the active rift zones. The blocks deform internally by the widespread reactivation of spreading-related faults and zones of weakness along dike margins. The sense of slip on these rift-parallel strike-slip faults is inconsistent with transform-fault deformation. These various deformation features as well as subaxial subsidence that accommodate the thickening of the volcanic upper crustal units are probably confined to the brittle, seismogenic, upper 10 km of the crust. At least beneath the active rift zones, the upper crust is probably decoupled from hot, mechanically weak middle and lower gabbroic crust resulting in a broad plate boundary zone between the diverging lithosphere plates. Similar processes may occur at other types of propagating spreading centers and magmatic rifts.

A geophysical investigation of shallow deformation along an anomalous section of the Wasatch fault zone, Utah, USA

USGS Publications Warehouse

McBride, J.H.; Stephenson, W.J.; Thompson, T.J.; Harper, M.P.; Eipert, A.A.; Hoopes, J.C.; Tingey, D.G.; Keach, R.W.; Okojie-Ayoro, A. O.; Gunderson, K.L.; Meirovitz, C.D.; Hicks, T.C.; Spencer, C.J.; Yaede, J.R.; Worley, D.M.

2008-01-01

We report the results of a geophysical study of the Wasatch fault zone near the Provo and Salt Lake City segment boundary. This area is anomalous because the fault zone strikes more east-west than north-south. Vibroseis was used to record a common mid-point (CMP) profile that provides information to depths of ???500 m. A tomographic velocity model, derived from first breaks, constrained source and receiver static corrections; this was required due to complex terrain and significant lateral velocity contrasts. The profile reveals an ???250-m-wide graben in the hanging wall of the main fault that is associated with both synthetic and antithetic faults. Faults defined by apparent reflector offsets propagate upward toward topographic gradients. Faults mapped from a nearby trench and the seismic profile also appear to correlate with topographic alignments on LiDAR gradient maps. The faults as measured in the trench show a wide range of apparent dips, 20??-90??, and appear to steepen with depth on the seismic section. Although the fault zone is likely composed of numerous small faults, the broad asymmetric structure in the hanging wall is fairly simple and dominated by two inward-facing ruptures. Our results indicate the feasibility of mapping fault zones in rugged terrain and complex near-surface geology using low-frequency vibroseis. Further, the integration of geologic mapping and seismic reflection can extend surface observations in areas where structural deformation is obscured by poorly stratified or otherwise unmappable deposits. Therefore, the vibroseis technique, when integrated with geological information, provides constraints for assessing geologic hazards in areas of potential development.

Quantitative analysis of seismic trapped waves in the rupture zone of the Landers, 1992, California earthquake: Evidence for a shallow trapping structure

NASA Astrophysics Data System (ADS)

Peng, Z.; Ben-Zion, Y.; Michael, A. J.; Zhu, L.

2002-12-01

Waveform modeling of seismic fault zone (FZ) trapped waves has been claimed to provide a high resolution imaging of FZ structure at seismogenic depth. We analyze quantitatively a waveform data set generated by 238 Landers aftershocks recorded by a portable seismic array (Lee, 1999). The array consists of 33 three-component L-22 seismometers, 22 of which on a line crossing the surface rupture zone of the mainshock. A subset of 93 aftershocks were also recorded by the Southern California Seismic Network, while the other events were recorded only by the FZ array. We locate the latter subset of events with a "grid-search relocation method" using accurately picked P and S arrival times, a half-space velocity model, and back-azimuth adjustment to correct the effect of low velocity FZ material on phase arrivals. Next we determine the quality of FZ trapped wave generation from the ratio of trapped waves to S-wave energy for stations relatively close to and far from the FZ. Energy ratios exceeding 4, between 2 and 4, and less than 2, are assigned quality A, B, and C of trapped wave generation. We find that about 70% of nearby events with S-P time less than 2 sec, including many clearly off the fault, generate FZ trapped waves with quality A or B. This distribution is in marked contrast with previous claims that trapped waves at Landers are generated only by sources close to or inside the fault zone (Li et al., 1994, 2000). The existence of trapped waves due to sources outside the Landers rupture zone indicates that the generating structure is shallow, as demonstrated in recent 3D calculations of wave propagation in irregular FZ structures (Fohrmann et al., 2002). The time difference between the S arrivals and trapped wave group does not grow systematically with increasing source-receiver distance along the fault, in agreement with the above conclusion. The dispersion of trapped waves at Landers is rather weak, again suggesting a short propagation distance inside the low velocity FZ material. To put additional constraints on properties of the shallow trapping structure at Landers, we modeled FZ trapped waves with a genetic inversion algorithm (Michael and Ben-Zion, 2002) using the 2D analytical solution of Ben-Zion and Aki (1990) and Ben-Zion (1998) for a uniform FZ structure. The synthetic waveform modeling indicates an effective FZ waveguide with depth of about 3-5 km, width on the order of 200 m, shear velocity reduction relative to the host rock of about 40-50%, and S wave quality factor of about 30. The modeling also shows that the waveguide is not centered at the exposed fault trace (station C00), but at a distance of about 100 m east of C00. Shallow trapping structures with similar properties appear to characterize also the Karadere-Duzce branch of the north Anatolian fault (Ben-Zion et al., 2002) and the Parkfield segment of the San Andreas fault (Michael and Ben-Zion, 2002; Korneev et al., 2002).

A New Look at Spreading in Iceland: Propagating Rifts, Migrating Transform Faults, and Microplate Tectonics

NASA Astrophysics Data System (ADS)

Karson, J.; Horst, A. J.; Nanfito, A.

2011-12-01

Iceland has long been used as an analog for studies of seafloor spreading. Despite its thick (~25 km) oceanic crust and subaerial lavas, many features associated with accretion along mid-ocean ridge spreading centers, and the processes that generate them, are well represented in the actively spreading Neovolcanic Zone and deeply glaciated Tertiary crust that flanks it. Integrated results of structural and geodetic studies show that the plate boundary zone on Iceland is a complex array of linked structures bounding major crustal blocks or microplates, similar to oceanic microplates. Major rift zones propagate N and S from the hotspot centered beneath the Vatnajökull icecap in SE central Iceland. The southern propagator has extended southward beyond the South Iceland Seismic Zone transform fault to the Westman Islands, resulting in abandonment of the Eastern Rift Zone. Continued propagation may cause abandonment of the Reykjanes Ridge. The northern propagator is linked to the southern end of the receding Kolbeinsey Ridge to the north. The NNW-trending Kerlingar Pseudo-fault bounds the propagator system to the E. The Tjörnes Transform Fault links the propagator tip to the Kolbeinsey Ridge and appears to be migrating northward in incremental steps, leaving a swath of deformed crustal blocks in its wake. Block rotations, concentrated mainly to the west of the propagators, are clockwise to the N of the hotspot and counter-clockwise to the S, possibly resulting in a component of NS divergence across EW-oriented rift zones. These rotations may help accommodate adjustments of the plate boundary zone to the relative movements of the N American and Eurasian plates. The rotated crustal blocks are composed of highly anisotropic crust with rift-parallel internal fabric generated by spreading processes. Block rotations result in reactivation of spreading-related faults as major rift-parallel, strike-slip faults. Structural details found in Iceland can help provide information that is difficult or impossible to obtain in propagating systems of the deep seafloor.

Self-healing slip pulses in dynamic rupture models due to velocity-dependent strength

USGS Publications Warehouse

Beeler, N.M.; Tullis, T.E.

1996-01-01

Seismological observations of short slip duration on faults (short rise time on seismograms) during earthquakes are not consistent with conventional crack models of dynamic rupture and fault slip. In these models, the leading edge of rupture stops only when a strong region is encountered, and slip at an interior point ceases only when waves from the stopped edge of slip propagate back to that point. In contrast, some seismological evidence suggests that the duration of slip is too short for waves to propagate from the nearest edge of the ruptured surface, perhaps even if the distance used is an asperity size instead of the entire rupture dimension. What controls slip duration, if not dimensions of the fault or of asperities? In this study, dynamic earthquake rupture and slip are represented by a propagating shear crack. For all propagating shear cracks, slip velocity is highest near the rupture front, and at a small distance behind the rupture front, the slip velocity decreases. As pointed out by Heaton (1990), if the crack obeys a negative slip-rate-dependent strength relation, the lower slip velocity behind the rupture front will lead to strengthening that further reduces the velocity, and under certain circumstances, healing of slip can occur. The boundary element method of Hamano (1974) is used in a program adapted from Andrews (1985) for numerical simulations of mode II rupture with two different velocity-dependent strength functions. For the first function, after a slip-weakening displacement, the crack follows an exponential velocity-weakening relation. The characteristic velocity V0 of the exponential determines the magnitude of the velocity-dependence at dynamic velocities. The velocity-dependence at high velocity is essentially zero when V0 is small and the resulting slip velocity distribution is similar to slip weakening. If V0 is larger, rupture propagation initially resembles slip-weakening, but spontaneous healing occurs behind the rupture front. The rise time and rupture propagation velocity depend on the choice of constitutive parameters. The second strength function is a natural log velocity-dependent form similar to constitutive laws that fit experimental rock friction data at lower velocities. Slip pulses also arise with this function. For a reasonable choice of constitutive parameters, slip pulses with this function do not propagate at speeds greater than the Raleighwave velocity. The calculated slip pulses are similar in many aspects to seismic observations of short rise time. In all cases of self-healing slip pulses, the residual stress increases with distance behind the trailing edge of the pulse so that the final stress drop is much less than the dynamic stress drop, in agreement with the model of Brune (1976) and some recent seismological observations of rupture.

Stress interaction at the Lazufre volcanic region, as constrained by InSAR, seismic tomography and boundary element modelling

NASA Astrophysics Data System (ADS)

Nikkhoo, Mehdi; Walter, Thomas R.; Lundgren, Paul; Spica, Zack; Legrand, Denis

2016-04-01

The Azufre-Lastarria volcanic complex in the central Andes has been recognized as a major region of magma intrusion. Both deep and shallow inflating reservoirs inferred through InSAR time series inversions, are the main sources of a multi-scale deformation accompanied by pronounced fumarolic activity. The possible interactions between these reservoirs, as well as the path of propagating fluids and the development of their pathways, however, have not been investigated. Results from recent seismic noise tomography in the area show localized zones of shear wave velocity anomalies, with a low shear wave velocity region at 1 km depth and another one at 4 km depth beneath Lastarria. Although the inferred shallow zone is in a good agreement with the location of the shallow deformation source, the deep zone does not correspond to any deformation source in the area. Here, using the boundary element method (BEM), we have performed an in-depth continuum mechanical investigation of the available ascending and descending InSAR data. We modelled the deep source, taking into account the effect of topography and complex source geometry on the inversion. After calculating the stress field induced by this source, we apply Paul's criterion (a variation on Mohr-Coulomb failure) to recognize locations that are liable for failure. We show that the locations of tensile and shear failure almost perfectly coincide with the shallow and deep anomalies as identified by shear wave velocity, respectively. Based on the stress-change models we conjecture that the deep reservoir controls the development of shallower hydrothermal fluids; a hypothesis that can be tested and applied to other volcanoes.

Group velocity of the light pulse in an open V-type system

NASA Astrophysics Data System (ADS)

Li, Jingjuan; Fan, Xijun; Tian, Shufen; Liu, Chengpu; Gong, Shangqing; Xu, Zhizhan

2007-04-01

We investigate the group velocity of the probe light pulse in an open V-type system with spontaneously generated coherence. We find that, not only varying the relative phase between the probe and driving pulses can but varying the atomic exit rate or incoherent pumping rate also can manipulate dramatically the group velocity, even make the pulse propagation switching from subluminal to superluminal; the subliminal propagation can be companied with gain or absorption, but the superluminal propagation is always companied with absorption.

Essential role of axonal VGSC inactivation in time-dependent deceleration and unreliability of spike propagation at cerebellar Purkinje cells

PubMed Central

2014-01-01

Background The output of the neuronal digital spikes is fulfilled by axonal propagation and synaptic transmission to influence postsynaptic cells. Similar to synaptic transmission, spike propagation on the axon is not secure, especially in cerebellar Purkinje cells whose spiking rate is high. The characteristics, mechanisms and physiological impacts of propagation deceleration and infidelity remain elusive. The spike propagation is presumably initiated by local currents that raise membrane potential to the threshold of activating voltage-gated sodium channels (VGSC). Results We have investigated the natures of spike propagation and the role of VGSCs in this process by recording spikes simultaneously on the somata and axonal terminals of Purkinje cells in cerebellar slices. The velocity and fidelity of spike propagation decreased during long-lasting spikes, to which the velocity change was more sensitive than fidelity change. These time-dependent deceleration and infidelity of spike propagation were improved by facilitating axonal VGSC reactivation, and worsen by intensifying VGSC inactivation. Conclusion Our studies indicate that the functional status of axonal VGSCs is essential to influencing the velocity and fidelity of spike propagation. PMID:24382121

Infrasound propagation in tropospheric ducts and acoustic shadow zones.

PubMed

de Groot-Hedlin, Catherine D

2017-10-01

Numerical computations of the Navier-Stokes equations governing acoustic propagation are performed to investigate infrasound propagation in the troposphere and into acoustic shadow zones. An existing nonlinear finite-difference, time-domain (FDTD) solver that constrains input sound speed models to be axisymmetric is expanded to allow for advection and rigid, stair-step topography. The FDTD solver permits realistic computations along a given azimuth. It is applied to several environmental models to examine the effects of nonlinearity, topography, advection, and two-dimensional (2D) variations in wind and sound speeds on the penetration of infrasound into shadow zones. Synthesized waveforms are compared to a recording of a rocket motor fuel elimination event at the Utah Test and Training Range. Results show good agreement in the amplitude, duration, and spectra of synthesized and recorded waveforms for propagation through 2D atmospheric models whether or not topography, advection, or nonlinearity is explicitly included. However, infrasound propagation through a one-dimensional, range-averaged, atmospheric model yields waveforms with lower amplitudes and frequencies, suggesting that small-scale atmospheric variability causes significant scatter within the troposphere, leading to enhanced infrasound penetration into shadow zones. Thus, unresolved fine-scale atmospheric dynamics are not required to explain infrasound propagation into shadow zones.

Quantifying strain partitioning between magmatic and amagmatic portions of the Afar triple junction of Ethiopia and Djibouti through use of contemporary and late Quaternary extension rates

NASA Astrophysics Data System (ADS)

Polun, S. G.; Hickcox, K.; Tesfaye, S.; Gomez, F. G.

2016-12-01

The central Afar rift in Ethiopia and Djibouti is a zone of accommodation between the onshore propagations of the Gulf of Aden and Red Sea oceanic spreading centers forming part of the Afar triple junction that divides the Arabia, Nubia, and Somalia plates. While extension in the onshore magmatic propagators is accommodated through magmatism and associated faulting, extension in the central Afar is accommodated solely by large and small faults. The contributions of these major faults to the overall strain budget can be well characterized, but smaller faults are more difficult to quantify. Sparse GPS data covering the region constrain the total extension budget across the diffuse triple junction zone. Late Quaternary slip rates for major faults in Hanle, Dobe, Guma, and Immino grabens were estimated using the quantitative analysis of faulted landforms. This forms a nearly complete transect from the onshore propagation of the Red Sea rift in Tendaho graben and the onshore propagation of the Gulf of Aden rift at Manda Inakir. Field surveying was accomplished using a combination of electronic distance measurer profiling and low altitude aerial surveying. Age constraints are provided from the Holocene lacustrine history or through terrestrial cosmogenic nuclide (TCN) dating of the faulted geomorphic surface. Along this transect, late Quaternary slip rates of major faults appear to accommodate 25% of the total horizontal stretching rate between the southern margin of Tendaho graben and the Red Sea coast, as determined from published GPS velocities. This constrains the proportion of total extension between Nubia and Arabia that is accommodated through major faulting in the central Afar, compared to the magmatism and associated faulting of the magmatic propagators elsewhere in the triple junction. Along the transect, individual fault slip rates decrease from the southeast to the northwest, suggesting a `Crank-Arm' model may be more applicable to explain the regional kinematics and the evolution of the triple junction.

Frictional properties of silicic to calcareous ooze on the Cocos Plate entering the Costa Rica Subduction Zone

NASA Astrophysics Data System (ADS)

Tsutsumi, A.; Kameda, J.; Ujiie, K.

2012-12-01

Here we report experimental results on the frictional properties of the cover sediments on the Cocos plate incoming into the erosive Costa Rica subduction zone. Mechanical properties of the incoming sediments to subduction plate boundaries are essential to constrain subduction-related faulting processes. However, knowledge of the frictional properties of sediments composed of abundant biogenic component, such as spicules, diatoms, and radiolarians are limited. Experimental samples were silicic to calcareous ooze collected at a reference site (Site U1381) off shore Osa Peninsula during IODP Expedition 334 (Vannucchi et al., 2012). To be used in the experiments, the discrete samples was disaggregated, oven dried at 60 degrees centigrade for 24 hours. The experimental fault is composed of a 24.9 mm diameter cylinder of gabbro cut perpendicularly to the cylinder axis in two halves that are ground to obtain rough wall surfaces, and re-assembled with an intervening thin layer (~1.0 mm) disaggregated sample. Frictional experiments have been performed using a rotary-shear friction testing machine, at normal stresses up to 5 MPa, over a range of slip velocities from 0.0026 mm/s to 1.3 m/s, with more than ~150 mm of displacements for water saturated condition. Experimental results reveal that friction values at slow slip velocities (v < ~30 mm/s) are about ~0.7, of which level is comparable to the typically reported friction values for rocks. The experimental faults exhibited velocity-weakening at v < 0.3 mm/s and neutral to velocity-strengthening at 0.3 < v < ~3 mm/s. At higher velocities (v > ~30 mm/s), steady state friction decreases dramatically. For example, at a velocity of 260 mm/s, the friction coefficient for samples U1381A-9R and -10R show a gradual decrease with a large weakening displacement toward the establishment of a nearly constant level of friction at ~0.1. The velocity weakening behavior at slow velocities could provide a condition to initiate unstable fault motion at shallow depths along the subduction channel if the input sediments are incorporated into faulting. On the contrary, neutral to velocity strengthening behavior observed for intermediate velocities could stabilize the propagation process of earthquake nuclei that emerges in the velocity weakening portion along the fault. It is important to note also that a dramatic slip weakening at velocities of v > ~30 mm/s characterizes the frictional behavior of the examined input sediments to the Costa Rica subduction zone. The relatively slower velocity condition for the onset of high-velocity weakening and the extremely low friction values (~0.1) observed at high velocities are comparable to the frictional properties reported for silicic fault (e.g., Goldsby and Tullis, 2002, GRL; Hayashi and Tsutsumi, 2010,GRL). Presented frictional properties of the incoming sediments may offer an important constraint for improving models of subduction-related faulting processes within the Costa Rica subduction channel.

Ultrasound imaging of propagation of myocardial contraction for non-invasive identification of myocardial ischemia

NASA Astrophysics Data System (ADS)

Matsuno, Yuya; Taki, Hirofumi; Yamamoto, Hiroaki; Hirano, Michinori; Morosawa, Susumu; Shimokawa, Hiroaki; Kanai, Hiroshi

2017-07-01

Non-invasive identification of ischemic regions is important for diagnosis and treatment of myocardial infarction. In the present study, ultrasound measurement was applied to the interventricular septum of three open-chest swine hearts. The properties of the myocardial contraction response of the septum were compared between normal and acute ischemic conditions, where the acute ischemic condition of the septum originated from direct avascularization of the left anterior descending (LAD) coronary artery. The result showed that the contraction response propagated from the basal side to the apical side along the septum. The estimated propagation velocities in the normal and acute ischemic conditions were 3.6 and 1.9 m/s, respectively. This finding indicates that acute ischemia which occurred 5 s after the avascularization of the LAD promptly suppressed the propagation velocity through the ventricular septum to about half the normal velocity. It was suggested that the myocardial ischemic region could be identified using the difference in the propagation velocity of the myocardial response to contraction.

Large‐displacement, hydrothermal frictional properties of DFDP‐1 fault rocks, Alpine Fault, New Zealand: Implications for deep rupture propagation

PubMed Central

Boulton, C.; Toy, V. G.; Townend, J.; Sutherland, R.

2016-01-01

Abstract The Alpine Fault, New Zealand, is a major plate‐bounding fault that accommodates 65–75% of the total relative motion between the Australian and Pacific plates. Here we present data on the hydrothermal frictional properties of Alpine Fault rocks that surround the principal slip zones (PSZ) of the Alpine Fault and those comprising the PSZ itself. The samples were retrieved from relatively shallow depths during phase 1 of the Deep Fault Drilling Project (DFDP‐1) at Gaunt Creek. Simulated fault gouges were sheared at temperatures of 25, 150, 300, 450, and 600°C in order to determine the friction coefficient as well as the velocity dependence of friction. Friction remains more or less constant with changes in temperature, but a transition from velocity‐strengthening behavior to velocity‐weakening behavior occurs at a temperature of T = 150°C. The transition depends on the absolute value of sliding velocity as well as temperature, with the velocity‐weakening region restricted to higher velocity for higher temperatures. Friction was substantially lower for low‐velocity shearing (V < 0.3 µm/s) at 600°C, but no transition to normal stress independence was observed. In the framework of rate‐and‐state friction, earthquake nucleation is most likely at an intermediate temperature of T = 300°C. The velocity‐strengthening nature of the Alpine Fault rocks at higher temperatures may pose a barrier for rupture propagation to deeper levels, limiting the possible depth extent of large earthquakes. Our results highlight the importance of strain rate in controlling frictional behavior under conditions spanning the classical brittle‐plastic transition for quartzofeldspathic compositions. PMID:27610290

Spatio-temporal propagation of cascading overload failures in spatially embedded networks

NASA Astrophysics Data System (ADS)

Zhao, Jichang; Li, Daqing; Sanhedrai, Hillel; Cohen, Reuven; Havlin, Shlomo

2016-01-01

Different from the direct contact in epidemics spread, overload failures propagate through hidden functional dependencies. Many studies focused on the critical conditions and catastrophic consequences of cascading failures. However, to understand the network vulnerability and mitigate the cascading overload failures, the knowledge of how the failures propagate in time and space is essential but still missing. Here we study the spatio-temporal propagation behaviour of cascading overload failures analytically and numerically on spatially embedded networks. The cascading overload failures are found to spread radially from the centre of the initial failure with an approximately constant velocity. The propagation velocity decreases with increasing tolerance, and can be well predicted by our theoretical framework with one single correction for all the tolerance values. This propagation velocity is found similar in various model networks and real network structures. Our findings may help to predict the dynamics of cascading overload failures in realistic systems.

Relationship between directions of wave and energy propagation for cold plasma waves

NASA Technical Reports Server (NTRS)

Musielak, Zdzislaw E.

1986-01-01

The dispersion relation for plasma waves is considered in the 'cold' plasma approximation. General formulas for the dependence of the phase and group velocities on the direction of wave propagation with respect to the local magnetic field are obtained for a cold magnetized plasma. The principal cold plasma resonances and cut-off frequencies are defined for an arbitrary angle and are used to establish basic regimes of frequency where the cold plasma waves can propagate or can be evanescent. The relationship between direction of wave and energy propagation, for cold plasma waves in hydrogen atmosphere, is presented in the form of angle diagrams (angle between group velocity and magnetic field versus angle between phase velocity and magnetic field) and polar diagrams (also referred to as 'Friedrich's diagrams') for different directions of wave propagation. Morphological features of the diagrams as well as some critical angles of propagation are discussed.

Spatio-temporal propagation of cascading overload failures in spatially embedded networks

PubMed Central

Zhao, Jichang; Li, Daqing; Sanhedrai, Hillel; Cohen, Reuven; Havlin, Shlomo

2016-01-01

Different from the direct contact in epidemics spread, overload failures propagate through hidden functional dependencies. Many studies focused on the critical conditions and catastrophic consequences of cascading failures. However, to understand the network vulnerability and mitigate the cascading overload failures, the knowledge of how the failures propagate in time and space is essential but still missing. Here we study the spatio-temporal propagation behaviour of cascading overload failures analytically and numerically on spatially embedded networks. The cascading overload failures are found to spread radially from the centre of the initial failure with an approximately constant velocity. The propagation velocity decreases with increasing tolerance, and can be well predicted by our theoretical framework with one single correction for all the tolerance values. This propagation velocity is found similar in various model networks and real network structures. Our findings may help to predict the dynamics of cascading overload failures in realistic systems. PMID:26754065

Theoretical and experimental studies of the waveforms associated with stratospheric infrasonic returns

NASA Astrophysics Data System (ADS)

Waxler, R.; Talmadge, C. L.; Blom, P.

2009-12-01

Theory predicts that for ground to ground infrasound propagation along paths which travel downwind, relative to the stratospheric jet, there is a shadow zone which ends about 200 km from the source where the first return from the stratosphere strikes the earth. With increasing range the single stratospheric arrival splits into two distinct arrivals, a fast arrival with the trace velocity of the effective sound speed at the stratopause, and a slower arrival with the trace velocity of the sound speed on the ground. To test the theory we have deployed eight infrasound arrays along an approximate line directly west of the site of the US Navy's Trident Missile rocket motor eliminations. The arrays were deployed during the summer of 2009 spaced roughly 10 km apart along a segment from 180 to 260 km west of the site. Comparisons between the theoretical predictions and the received data will be presented.

Ground motion hazard from supershear rupture

USGS Publications Warehouse

Andrews, D.J.

2010-01-01

An idealized rupture, propagating smoothly near a terminal rupture velocity, radiates energy that is focused into a beam. For rupture velocity less than the S-wave speed, radiated energy is concentrated in a beam of intense fault-normal velocity near the projection of the rupture trace. Although confined to a narrow range of azimuths, this beam diverges and attenuates. For rupture velocity greater than the S-wave speed, radiated energy is concentrated in Mach waves forming a pair of beams propagating obliquely away from the fault. These beams do not attenuate until diffraction becomes effective at large distance. Events with supershear and sub-Rayleigh rupture velocity are compared in 2D plane-strain calculations with equal stress drop, fracture energy, and rupture length; only static friction is changed to determine the rupture velocity. Peak velocity in the sub-Rayleigh case near the termination of rupture is larger than peak velocity in the Mach wave in the supershear case. The occurrence of supershear rupture propagation reduces the most intense peak ground velocity near the fault, but it increases peak velocity within a beam at greater distances.

The role of chemical processes and brittle deformation during shear zone formation and its potential geophysical implications

NASA Astrophysics Data System (ADS)

Goncalves, Philippe; Leydier, Thomas; Mahan, Kevin; Albaric, Julie; Trap, Pierre; Marquer, Didier

2017-04-01

Ductile shear zones in the middle and lower continental crust are the locus of interactions between mechanical and chemical processes. Chemical processes encompass metamorphic reactions, fluid-rock interactions, fluid flow and chemical mass-transfer. Studying these processes at the grain scale, and even the atom scale, on exposed inactive shear zones can give insights into large-scale geodynamics phenomena (e.g. crustal growth and mountain building through the reconstruction of P-T-t-D-Ɛ evolutionary paths. However, other major issues in earth sciences can be tackled through these studies as well. For instance, the mechanism of fluid flow and mass transfer in the deep crust where permeability should be small and transient is still largely debated. Studying exhumed inactive shear zones can also help to interpret several new geophysical observations like (1) the origin of tremor and very low frequency earthquakes observed in the ductile middle and lower crust, (2) mechanisms for generating slow slip events and (3) the physical origin of puzzling crustal anisotropy observed in major active crustal shear zones. In this contribution, we present a collection of data (deformation, petrology, geochemistry, microtexture) obtained on various shear zones from the Alps that were active within the viscous regime (T > 450°C). Our observations show that the development of a shear zone, from its nucleation to its growth and propagation, is not only governed by ductile deformation coeval with reactions but also involves brittle deformation. Although brittle deformation is a very short-lived phenomenon, our petrological and textural observations show that brittle failure is also associated with fluid flow, mass transfer, metasomatic reactions and recrystallization. We speculate that the fluids and the associated mineralogical changes involved during this brittle failure in the ductile crust might play a role in earthquake / tremor triggering below the brittle - ductile transition. Furthermore, the occurrence of micro-fracturing in the ductile crust must have an influence on elastic wave propagation. While in the upper crust, fractures are believed to be the primary contributor to seismic anisotropy, at high pressure, the intrinsic rock Vp and Vs velocities are largely a function of the shape and crystallographic preferred orientation of minerals. However, if microfracturing is involved during ductile deformation, it may have a stronger influence on seismic properties (velocity and anisotropy) than the SPO and CPO of the main mineral phases, particularly if the microfractures are preferentially oriented. Thus, in major active ductile shear zones, like the Main Himalayan Thrust, the speculated transient but pervasive micro-fracturing during ongoing ductile deformation should be considered when interpreting seismic anisotropy. Finding evidences for brittle deformation, and associated fluid flow, in the ductile crust is a major challenge because many of these textural and mineralogical features tend to be obliterated by the pro-eminent ductile deformation. However, in order to fully understand the causes of some of these geophysical observations, the chemical and physical characterization of exhumed "fossil" ductile shear zones remains essential.

Modeling propagation of infrasound signals observed by a dense seismic network.

PubMed

Chunchuzov, I; Kulichkov, S; Popov, O; Hedlin, M

2014-01-01

The long-range propagation of infrasound from a surface explosion with an explosive yield of about 17.6 t TNT that occurred on June 16, 2008 at the Utah Test and Training Range (UTTR) in the western United States is simulated using an atmospheric model that includes fine-scale layered structure of the wind velocity and temperature fields. Synthetic signal parameters (waveforms, amplitudes, and travel times) are calculated using parabolic equation and ray-tracing methods for a number of ranges between 100 and 800 km from the source. The simulation shows the evolution of several branches of stratospheric and thermospheric signals with increasing range from the source. Infrasound signals calculated using a G2S (ground-to-space) atmospheric model perturbed by small-scale layered wind velocity and temperature fluctuations are shown to agree well with recordings made by the dense High Lava Plains seismic network located at an azimuth of 300° from UTTR. The waveforms of calculated infrasound arrivals are compared with those of seismic recordings. This study illustrates the utility of dense seismic networks for mapping an infrasound field with high spatial resolution. The parabolic equation calculations capture both the effect of scattering of infrasound into geometric acoustic shadow zones and significant temporal broadening of the arrivals.

Effect of slow energy releasing on divergent detonation of Insensitive High Explosives

NASA Astrophysics Data System (ADS)

Hu, Xiaomian; Pan, Hao; Huang, Yong; Wu, Zihui

2014-03-01

There exists a slow energy releasing (SER) process in the slow reaction zone located behind the detonation wave due to the carbon cluster in the detonation products of Insensitive High Explosives (IHEs), and the process will affect the divergent detonation wave's propagation and the driving process of the explosives. To study the potential effect, a new artificial burn model including the SER process based on the programmed burn model is proposed in the paper. Quasi-steady analysis of the new model indicates that the nonlinearity of the detonation speed as a function of front curvature owes to the significant change of the reaction rate and the reaction zone length at the sonic state. What's more, in simulating the detonation of IHE JB-9014, the new model including the slow reaction can predict a slower jump-off velocity, in good agreement with the result of the test.

Observation of acoustic Dirac-like cone and double zero refractive index

PubMed Central

Dubois, Marc; Shi, Chengzhi; Zhu, Xuefeng; Wang, Yuan; Zhang, Xiang

2017-01-01

Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre. PMID:28317927

TURBULENCE, TRANSPORT, AND WAVES IN OHMIC DEAD ZONES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gole, Daniel; Simon, Jacob B.; Armitage, Philip J.

We use local numerical simulations to study a vertically stratified accretion disk with a resistive mid-plane that damps magnetohydrodynamic (MHD) turbulence. This is an idealized model for the dead zones that may be present at some radii in protoplanetary and dwarf novae disks. We vary the relative thickness of the dead and active zones to quantify how forced fluid motions in the dead zone change. We find that the residual Reynolds stress near the mid-plane decreases with increasing dead zone thickness, becoming negligible in cases where the active to dead mass ratio is less than a few percent. This impliesmore » that purely Ohmic dead zones would be vulnerable to episodic accretion outbursts via the mechanism of Martin and Lubow. We show that even thick dead zones support a large amount of kinetic energy, but this energy is largely in fluid motions that are inefficient at angular momentum transport. Confirming results from Oishi and Mac Low, the perturbed velocity field in the dead zone is dominated by an oscillatory, vertically extended circulation pattern with a low frequency compared to the orbital frequency. This disturbance has the properties predicted for the lowest order r mode in a hydrodynamic disk. We suggest that in a global disk similar excitations would lead to propagating waves, whose properties would vary with the thickness of the dead zone and the nature of the perturbations (isothermal or adiabatic). Flows with similar amplitudes would buckle settled particle layers and could reduce the efficiency of pebble accretion.« less

Structural control on the Tohoku earthquake rupture process investigated by 3D FEM, tsunami and geodetic data

PubMed Central

Romano, F.; Trasatti, E.; Lorito, S.; Piromallo, C.; Piatanesi, A.; Ito, Y.; Zhao, D.; Hirata, K.; Lanucara, P.; Cocco, M.

2014-01-01

The 2011 Tohoku earthquake (Mw = 9.1) highlighted previously unobserved features for megathrust events, such as the large slip in a relatively limited area and the shallow rupture propagation. We use a Finite Element Model (FEM), taking into account the 3D geometrical and structural complexities up to the trench zone, and perform a joint inversion of tsunami and geodetic data to retrieve the earthquake slip distribution. We obtain a close spatial correlation between the main deep slip patch and the local seismic velocity anomalies, and large shallow slip extending also to the North coherently with a seismically observed low-frequency radiation. These observations suggest that the friction controlled the rupture, initially confining the deeper rupture and then driving its propagation up to the trench, where it spreads laterally. These findings are relevant to earthquake and tsunami hazard assessment because they may help to detect regions likely prone to rupture along the megathrust, and to constrain the probability of high slip near the trench. Our estimate of ~40 m slip value around the JFAST (Japan Trench Fast Drilling Project) drilling zone contributes to constrain the dynamic shear stress and friction coefficient of the fault obtained by temperature measurements to ~0.68 MPa and ~0.10, respectively. PMID:25005351

Structural control on the Tohoku earthquake rupture process investigated by 3D FEM, tsunami and geodetic data.

PubMed

Romano, F; Trasatti, E; Lorito, S; Piromallo, C; Piatanesi, A; Ito, Y; Zhao, D; Hirata, K; Lanucara, P; Cocco, M

2014-07-09

The 2011 Tohoku earthquake (Mw = 9.1) highlighted previously unobserved features for megathrust events, such as the large slip in a relatively limited area and the shallow rupture propagation. We use a Finite Element Model (FEM), taking into account the 3D geometrical and structural complexities up to the trench zone, and perform a joint inversion of tsunami and geodetic data to retrieve the earthquake slip distribution. We obtain a close spatial correlation between the main deep slip patch and the local seismic velocity anomalies, and large shallow slip extending also to the North coherently with a seismically observed low-frequency radiation. These observations suggest that the friction controlled the rupture, initially confining the deeper rupture and then driving its propagation up to the trench, where it spreads laterally. These findings are relevant to earthquake and tsunami hazard assessment because they may help to detect regions likely prone to rupture along the megathrust, and to constrain the probability of high slip near the trench. Our estimate of ~40 m slip value around the JFAST (Japan Trench Fast Drilling Project) drilling zone contributes to constrain the dynamic shear stress and friction coefficient of the fault obtained by temperature measurements to ~0.68 MPa and ~0.10, respectively.

Laboratory Model of the Cardiovascular System for Experimental Demonstration of Pulse Wave Propagation

ERIC Educational Resources Information Center

Stojadinovic, Bojana; Nestorovic, Zorica; Djuric, Biljana; Tenne, Tamar; Zikich, Dragoslav; Žikic, Dejan

2017-01-01

The velocity by which a disturbance moves through the medium is the wave velocity. Pulse wave velocity is among the key parameters in hemodynamics. Investigation of wave propagation through the fluid-filled elastic tube has a great importance for the proper biophysical understanding of the nature of blood flow through the cardiovascular system.…

Langevin approach to a chemical wave front: Selection of the propagation velocity in the presence of internal noise

NASA Astrophysics Data System (ADS)

Lemarchand, A.; Lesne, A.; Mareschal, M.

1995-05-01

The reaction-diffusion equation associated with the Fisher chemical model A+B-->2A admits wave-front solutions by replacing an unstable stationary state with a stable one. The deterministic analysis concludes that their propagation velocity is not prescribed by the dynamics. For a large class of initial conditions the velocity which is spontaneously selected is equal to the minimum allowed velocity vmin, as predicted by the marginal stability criterion. In order to test the relevance of this deterministic description we investigate the macroscopic consequences, on the velocity and the width of the front, of the intrinsic stochasticity due to the underlying microscopic dynamics. We solve numerically the Langevin equations, deduced analytically from the master equation within a system size expansion procedure. We show that the mean profile associated with the stochastic solution propagates faster than the deterministic solution at a velocity up to 25% greater than vmin.

Review of critical flow rate, propagation of pressure pulse, and sonic velocity in two-phase media

NASA Technical Reports Server (NTRS)

Hsu, Y.

1972-01-01

For single-phase media, the critical discharge velocity, the sonic velocity, and the pressure pulse propagation velocity can be expressed in the same form by assuming isentropic, equilibria processes. In two-phase mixtures, the same concept is not valid due to the existence of interfacial transports of momentum, heat, and mass. Thus, the three velocities should be treated differently and separately for each particular condition, taking into account the various transport processes involved under that condition. Various attempts are reviewed to predict the critical discharge rate or the propagation velocities by considering slip ratio (momentum change), evaporation (mass and heat transport), flow pattern, etc. Experimental data were compared with predictions based on various theorems. The importance is stressed of the time required to achieve equilibrium as compared with the time available during the process, for example, of passing a pressure pulse.

40 CFR 146.67 - Operating requirements.

Code of Federal Regulations, 2011 CFR

2011-07-01

... fractures or propagate existing fractures in the injection zone. The owner or operator shall assure that the injection pressure does not initiate fractures or propagate existing fractures in the confining zone, nor...

40 CFR 146.67 - Operating requirements.

Code of Federal Regulations, 2013 CFR

2013-07-01

... fractures or propagate existing fractures in the injection zone. The owner or operator shall assure that the injection pressure does not initiate fractures or propagate existing fractures in the confining zone, nor...

40 CFR 146.67 - Operating requirements.

Code of Federal Regulations, 2014 CFR

2014-07-01

... fractures or propagate existing fractures in the injection zone. The owner or operator shall assure that the injection pressure does not initiate fractures or propagate existing fractures in the confining zone, nor...

40 CFR 146.67 - Operating requirements.

Code of Federal Regulations, 2012 CFR

2012-07-01

... fractures or propagate existing fractures in the injection zone. The owner or operator shall assure that the injection pressure does not initiate fractures or propagate existing fractures in the confining zone, nor...

A shallow fault-zone structure illuminated by trapped waves in the Karadere-Duzce branch of the North Anatolian Fault, western Turkey

USGS Publications Warehouse

Ben-Zion, Y.; Peng, Z.; Okaya, D.; Seeber, L.; Armbruster, J.G.; Ozer, N.; Michael, A.J.; Baris, S.; Aktar, M.

2003-01-01

We discuss the subsurface structure of the Karadere-Duzce branch of the North Anatolian Fault based on analysis of a large seismic data set recorded by a local PASSCAL network in the 6 months following the Mw = 7.4 1999 Izmit earthquake. Seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long-period oscillations in both P- and S-wave trains that do not exist in nearby off-fault stations. Examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone. The anomalous features in fault-zone seismograms produced by events not necessarily in the fault may be referred to generally as fault-zone-related site effects. The oscillatory shear wave trains after the direct S arrival in these seismograms are analysed as trapped waves propagating in a low-velocity fault-zone layer. The time difference between the S arrival and trapped waves group does not grow systematically with increasing source-receiver separation along the fault. These observations imply that the trapping of seismic energy in the Karadere-Duzce rupture zone is generated by a shallow fault-zone layer. Traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3-4 km. The synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m, a velocity decrease relative to the surrounding rock of approximately 50 per cent and an S-wave quality factor of 10-15. The results are supported by large 2-D and 3-D parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones. The inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower-type structure. The motion amplification associated with fault-zone-related site effects increases the seismic shaking hazard near fault-zone structures. The effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large.

Flow networks for Ocean currents

NASA Astrophysics Data System (ADS)

Tupikina, Liubov; Molkenthin, Nora; Marwan, Norbert; Kurths, Jürgen

2014-05-01

Complex networks have been successfully applied to various systems such as society, technology, and recently climate. Links in a climate network are defined between two geographical locations if the correlation between the time series of some climate variable is higher than a threshold. Therefore, network links are considered to imply heat exchange. However, the relationship between the oceanic and atmospheric flows and the climate network's structure is still unclear. Recently, a theoretical approach verifying the correlation between ocean currents and surface air temperature networks has been introduced, where the Pearson correlation networks were constructed from advection-diffusion dynamics on an underlying flow. Since the continuous approach has its limitations, i.e., by its high computational complexity, we here introduce a new, discrete construction of flow-networks, which is then applied to static and dynamic velocity fields. Analyzing the flow-networks of prototypical flows we find that our approach can highlight the zones of high velocity by degree and transition zones by betweenness, while the combination of these network measures can uncover how the flow propagates within time. We also apply the method to time series data of the Equatorial Pacific Ocean Current and the Gulf Stream ocean current for the changing velocity fields, which could not been done before, and analyse the properties of the dynamical system. Flow-networks can be powerful tools to theoretically understand the step from system's dynamics to network's topology that can be analyzed using network measures and is used for shading light on different climatic phenomena.

Three-dimensional long-period groundmotion simulations in the upper Mississippi embayment

USGS Publications Warehouse

Macpherson, K.A.; Woolery, E.W.; Wang, Z.; Liu, P.

2010-01-01

We employed a 3D velocity model and 3D wave propagation code to simulate long-period ground motions in the upper Mississippi embayment. This region is at risk from large earthquakes in the New Madrid seismic zone (NMSZ) and observational data are sparse, making simulation a valuable tool for predicting the effects of large events. We undertook these simulations to estimate the magnitude of shaking likely to occur and to investigate the influence of the 3D embayment structure and finite-fault mechanics on ground motions. There exist three primary fault zones in the NMSZ, each of which was likely associated with one of the main shocks of the 1811-12 earthquake triplet. For this study, three simulations have been conducted on each major segment, exploring the impact of different epicentral locations and rupture directions on ground motions. The full wave field up to a frequency of 0.5 Hz is computed on a 200 ?? 200 ?? 50-km 3 volume using a staggered-grid finite-difference code. Peak horizontal velocity and bracketed durations were calculated at the free surface. The NMSZ simulations indicate that for the considered bandwidth, finite-fault mechanics such as fault proximity, directivity effect, and slip distribution exert the most control on ground motions. The 3D geologic structure of the upper Mississippi embayment also influences ground motion with indications that amplification is induced by the sharp velocity contrast at the basin edge.

Off-fault heterogeneities promote supershear transition of dynamic mode II cracks

NASA Astrophysics Data System (ADS)

Albertini, Gabriele; Kammer, David S.

2017-08-01

The transition from sub-Rayleigh to supershear propagation of mode II cracks is a fundamental problem of fracture mechanics. It has extensively been studied in homogeneous uniform setups. When the applied shear load exceeds a critical value, transition occurs through the Burridge-Andrews mechanism at a well-defined crack length. However, velocity structures in geophysical conditions can be complex and affect the transition. Damage induced by previous earthquakes causes low-velocity zones surrounding mature faults and inclusions with contrasting material properties can be present at seismogenic depth. We relax the assumption of homogeneous media and investigate dynamic shear fracture in heterogeneous media using two-dimensional finite element simulations and a linear slip-weakening law. We analyze the role of heterogeneities in the elastic media, while keeping the frictional interface properties uniform. We show that supershear transition is possible due to the sole presence of favorable off-fault heterogeneities. Subcritical shear loads, for which propagation would remain permanently sub-Rayleigh in an equivalent homogeneous setup, will transition to supershear as a result of reflected waves. P wave reflected as S waves, followed by further reflections, affect the amplitude of the shear stress peak in front of the propagating crack, leading to supershear transition. A wave reflection model allows to uniquely describe the effect of off-fault inclusions on the shear stress peak. A competing mechanism of modified released potential energy affects transition and becomes predominant with decreasing distance between fault and inclusions. For inclusions at far distances, the wave reflection is the predominant mechanism.

Lateral heterogeneity and azimuthal anistropy of the upper mantle: Love and Rayleigh waves 100-250 sec

NASA Technical Reports Server (NTRS)

Tanimoto, T.; Anderson, D. L.

1983-01-01

The lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring Rayleigh and Love wave phase velocities in the period range 100-250 sec. Spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1=m=10. Slow regions are evident at the East Pacific rise, northeast Africa, Tibet, Tasman sea, southwestern North America and triple junctions in the Northern Atlantic and Indian oceans. Fast regions occur in Australia, western Pacific and the eastern Atlantic. Details which are not evident in previous studies include two fast regions in the central Pacific and the subduction zone in the Scotia Arc region. Inversion for azimuthal dependence showed (1) little correlation between the fast phase velocity directions and the plate motion vector in plate interiors, but (2) correlation of the fast direction with the perpendicular direction to trenches and ridges. Phase velocity is high when waves propagate perpendicular to these structures. Severe tradeoffs exist between heterogeneity and azimuthal dependence because of the yet unsatisfactory path coverage.

Lateral heterogeneity and azimuthal anisotropy of the upper mantle - Love and Rayleigh waves 100-250 sec

NASA Technical Reports Server (NTRS)

Tanimoto, T.; Anderson, D. L.

1985-01-01

The lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring Rayleigh and Love wave phase velocities in the period range 100-250 sec. Spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1=m=10. Slow regions are evident at the East Pacific rise, northeast Africa, Tibet, Tasman sea, southwestern North America and triple junctions in the Northern Atlantic and Indian oceans. Fast regions occur in Australia, western Pacific and the eastern Atlantic. Details which are not evident in previous studies include two fast regions in the central Pacific and the subduction zone in the Scotia Arc region. Inversion for azimuthal dependence showed (1) little correlation between the fast phase velocity directions and the plate motion vector in plate interiors, but (2) correlation of the fast direction with the perpendicular direction to trenches and ridges. Phase velocity is high when waves propagate perpendicular to these structures. Severe tradeoffs exist between heterogeneity and azimuthal dependence because of the yet unsatisfactory path coverage.

Geodynamic environments of ultra-slow spreading

NASA Astrophysics Data System (ADS)

Kokhan, Andrey; Dubinin, Evgeny

2015-04-01

Ultra-slow spreading is clearly distinguished as an outstanding type of crustal accretion by recent studies. Spreading ridges with ultra-slow velocities of extension are studied rather well. But ultra-slow spreading is characteristic feature of not only spreading ridges, it can be observed also on convergent and transform plate boundaries. Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on divergent plate boundaries: 1. On spreading ridges with ultra-slow spreading, both modern (f.e. Gakkel, South-West Indian, Aden spreading center) and ceased (Labrador spreading center, Aegir ridge); 2. During transition from continental rifting to early stages of oceanic spreading (all spreading ridges during incipient stages of their formation); 3. During incipient stages of formation of spreading ridges on oceanic crust as a result of ridge jumps and reorganization of plate boundaries (f.e. Mathematicians rise and East Pacific rise); 4. During propagation of spreading ridge into the continental crust under influence of hotspot (Aden spreading center and Afar triple junction), under presence of strike-slip faults preceding propagation (possibly, rift zone of California Bay). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on transform plate boundaries: 1. In transit zones between two "typical" spreading ridges (f.e. Knipovich ridge); 2. In semi strike-slip/extension zones on the oceanic crust (f.e. American-Antarctic ridge); 3. In the zones of local extension in regional strike-slip areas in pull-apart basins along transform boundaries (Cayman trough, pull-apart basins of the southern border of Scotia plate). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on convergent plate boundaries: 1. During back-arc rifting on the stage of transition into back-arc spreading (central part of Bransfield rift); 2. During back-arc inter-subduction spreading (Ayu trough, northern Fiji basin), 3. During diffuse back-arc spreading (area on the south-eastern border of Scotia sea), 4. During back-arc spreading under splitting of island arc (northern extremity of Mariana trough). Each of the geodynamic environments is characterized by peculiar topographic, geological and geophysical features forming under the same spreading velocities. Development of ultra-slow spreading in each of these environments results in formation of peculiar extension sedimentary basins.

Signal velocity and group velocity for an optical pulse propagating through a GaAs cavity.

PubMed

Centini, Marco; Bloemer, Mark; Myneni, Krishna; Scalora, Michael; Sibilia, Concita; Bertolotti, Mario; D'Aguanno, Giuseppe

2003-07-01

We present measurements of the signal and group velocities for chirped optical pulses propagating through a GaAs cavity. The signal velocity is based on a specified signal-to-noise ratio at the detector. Under our experimental conditions, the chirp substantially modifies the group velocity of the pulse, but leaves the signal velocity unaltered. At unity transmittance, the velocities are equal. In general, when the transmittance is less than unity, the group velocity is faster than the signal velocity. While the group velocity can be negative, the signal velocity is always less than c/n, where c is the speed of light in vacuum and n is the refractive index of GaAs. To our knowledge, this is the first measurement of both the group velocity and the signal velocity in any system.

Crustal structure of the Kaapvaal craton and its significance for early crustal evolution

NASA Astrophysics Data System (ADS)

James, David E.; Niu, Fenglin; Rokosky, Juliana

2003-12-01

High-quality seismic data obtained from a dense broadband array near Kimberley, South Africa, exhibit crustal reverberations of remarkable clarity that provide well-resolved constraints on the structure of the lowermost crust and Moho. Receiver function analysis of Moho conversions and crustal multiples beneath the Kimberley array shows that the crust is 35 km thick with an average Poisson's ratio of 0.25. The density contrast across the Moho is ˜15%, indicating a crustal density about 2.86 gm/cc just above the Moho, appropriate for felsic to intermediate rock compositions. Analysis of waveform broadening of the crustal reverberation phases suggests that the Moho transition can be no more than 0.5 km thick and the total variation in crustal thickness over the 2400 km 2 footprint of the array no more than 1 km. Waveform and travel time analysis of a large earthquake triggered by deep gold mining operations (the Welkom mine event) some 200 km away from the array yield an average crustal thickness of 35 km along the propagation path between the Kimberley array and the event. P- and S-wave velocities for the lowermost crust are modeled to be 6.75 and 3.90 km/s, respectively, with uppermost mantle velocities of 8.2 and 4.79 km/s, respectively. Seismograms from the Welkom event exhibit theoretically predicted but rarely observed crustal reverberation phases that involve reflection or conversion at the Moho. Correlation between observed and synthetic waveforms and phase amplitudes of the Moho reverberations suggests that the crust along the propagation path between source and receiver is highly uniform in both thickness and average seismic velocity and that the Moho transition zone is everywhere less than about 2 km thick. While the extremely flat Moho, sharp transition zone and low crustal densities beneath the region of study may date from the time of crustal formation, a more geologically plausible interpretation involves extensive crustal melting and ductile flow during the major craton-wide Ventersdorp tectonomagmatic event near the end of Archean time.

Fault Lubrication and Earthquake Propagation in Thermally Unstable Rocks

NASA Astrophysics Data System (ADS)

de Paola, Nicola; Hirose, Takehiro; Mitchell, Tom; di Toro, Giulio; Viti, Cecilia; Shimamoto, Toshiko

2010-05-01

During earthquake propagation in thermally unstable rocks, the frictional heat generated can induce thermal reactions which lead to chemical and physical changes in the slip zone. We performed laboratory friction experiments on thermally unstable minerals (gypsum, dolomite and calcite) at about 1 m/s slip velocities, more than 1 m displacements and calculated temperature rise above 500 C degrees. These conditions are typical during the propagation of large earthquakes. The main findings of our experimental work are: 1) Dramatic fault weakening is characterized by a dynamic frictional strength drop up to 90% of the initial static value in the Byerlee's range. 2) Seismic source parameters, calculated from our experimental results, match those obtained by modelling of seismological data from the 1997 Cofliorito earthquake nucleated in carbonate rocks in Italy (i.e. same rocks used in the friction experiments). Fault lubrication observed during the experiments is controlled by the superposition of multiple, thermally-activated, slip weakening mechanisms (e.g., flash heating, thermal pressurization and nanoparticle lubrication). The integration of mechanical and CO2 emission data, temperature rise calculations and XRPD analyses suggests that flash heating is not the main dynamic slip weakening process. This process was likely inhibited very soon (t < 1s) for displacements d < 0.20 m, when intense grain size reduction by both cataclastic and chemical/thermal processes took place. Conversely, most of the dynamic weakening observed was controlled by thermal pressurization and nanoparticle lubrication processes. The dynamic shear strength of experimental faults was reduced when fluids (CO2, H2O) were trapped and pressurized within the slip zone, in accord with the effective normal stress principle. The fluids were not initially present in the slip zone, but were released by decarbonation (dolomite and Mg-rich calcite) and dehydration (gypsum) reactions, both activated by frictional heating during seismic slip. The dynamic weakening effects of nanoparticles (e.g. powder lubrication) are still unclear due to the poorly understood mechanical properties of nanoparticles at high velocities and temperatures, typical of seismic slip. The experimental results improve our understanding of the controls exerted on the dynamic frictional strength of faults by the coseismic operation of chemical (mineral decomposition) and physical (grain size reduction, fluids release and pressurization) processes. The estimation of this parameter is out of the range of seismological studies, although it controls the magnitude of the stress drop, the seismic fault heat flow and the relative partitioning of the earthquake energy budget, which are all controversial and still debated issues in the scientific community.

Fault Lubrication and Earthquake Propagation in Thermally Unstable Rocks

NASA Astrophysics Data System (ADS)

de Paola, N.; Hirose, T.; Mitchell, T. M.; di Toro, G.; Viti, C.; Shimamoto, T.

2009-12-01

During earthquake propagation in thermally unstable rocks, the frictional heat generated can induce thermal reactions which lead to chemical and physical changes in the slip zone. We performed laboratory friction experiments on thermally unstable minerals (gypsum, dolomite and calcite) at about 1 m/s slip velocities, more than 1 m displacements and calculated temperature rise above 500 C degrees. These conditions are typical during the propagation of large earthquakes. The main findings of our experimental work are: 1) Dramatic fault weakening is characterized by a dynamic frictional strength drop up to 90% of the initial static value in the Byerlee’s range. 2) Seismic source parameters, calculated from our experimental results, match those obtained by modelling of seismological data from the 1997 Cofliorito earthquake nucleated in carbonate rocks in Italy (i.e. same rocks used in the friction experiments). Fault lubrication observed during the experiments is controlled by the superposition of multiple, thermally-activated, slip weakening mechanisms (e.g., flash heating, thermal pressurization and nanoparticle lubrication). The integration of mechanical and CO2 emission data, temperature rise calculations and XRPD analyses suggests that flash heating is not the main dynamic slip weakening process. This process was likely inhibited very soon (t < 1s) for displacements d < 0.20 m, when intense grain size reduction by both cataclastic and chemical/thermal processes took place. Conversely, most of the dynamic weakening observed was controlled by thermal pressurization and nanoparticle lubrication processes. The dynamic shear strength of experimental faults was reduced when fluids (CO2, H2O) were trapped and pressurized within the slip zone, in accord with the effective normal stress principle. The fluids were not initially present in the slip zone, but were released by decarbonation (dolomite and Mg-rich calcite) and dehydration (gypsum) reactions, both activated by frictional heating during seismic slip. The dynamic weakening effects of nanoparticles (e.g. powder lubrication) are still unclear due to the poorly understood mechanical properties of nanoparticles at high velocities and temperatures, typical of seismic slip. The experimental results improve our understanding of the controls exerted on the dynamic frictional strength of faults by the coseismic operation of chemical (mineral decomposition) and physical (grain size reduction, fluids release and pressurization) processes. The estimation of this parameter is out of the range of seismological studies, although it controls the magnitude of the stress drop, the seismic fault heat flow and the relative partitioning of the earthquake energy budget, which are all controversial and still debated issues in the scientific community.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khafizov, M.; Pakarinen, J.; He, L.

We report on imaging subsurface grain microstructure using picosecond ultrasonics. This approach relies on elastic anisotropy of crystalline materials where ultrasonic velocity depends on propagation direction relative to the crystal axes. Picosecond duration ultrasonic pulses are generated and detected using ultrashort light pulses. In materials that are transparent or semitransparent to the probe wavelength, the probe monitors GHz Brillouin oscillations. The frequency of these oscillations is related to the ultrasonic velocity and the optical index of refraction. Ultrasonic waves propagating across a grain boundary experience a change in velocity due to a change in crystallographic orientation relative to the ultrasonicmore » propagation direction. This change in velocity is manifested as a change in the Brillouin oscillation frequency. Using the ultrasonic propagation velocity, the depth of the interface can be determined from the location in time of the transition in oscillation frequency. An image of the grain boundary is obtained by scanning the beam along the surface. We demonstrate this volumetric imaging capability using a polycrystalline UO 2 sample. As a result, cross section liftout analysis of the grain boundaries using electron microscopy were used to verify our imaging results.« less

Critical Parameters of the Initiation Zone for Spontaneous Dynamic Rupture Propagation

NASA Astrophysics Data System (ADS)

Galis, M.; Pelties, C.; Kristek, J.; Moczo, P.; Ampuero, J. P.; Mai, P. M.

2014-12-01

Numerical simulations of rupture propagation are used to study both earthquake source physics and earthquake ground motion. Under linear slip-weakening friction, artificial procedures are needed to initiate a self-sustained rupture. The concept of an overstressed asperity is often applied, in which the asperity is characterized by its size, shape and overstress. The physical properties of the initiation zone may have significant impact on the resulting dynamic rupture propagation. A trial-and-error approach is often necessary for successful initiation because 2D and 3D theoretical criteria for estimating the critical size of the initiation zone do not provide general rules for designing 3D numerical simulations. Therefore, it is desirable to define guidelines for efficient initiation with minimal artificial effects on rupture propagation. We perform an extensive parameter study using numerical simulations of 3D dynamic rupture propagation assuming a planar fault to examine the critical size of square, circular and elliptical initiation zones as a function of asperity overstress and background stress. For a fixed overstress, we discover that the area of the initiation zone is more important for the nucleation process than its shape. Comparing our numerical results with published theoretical estimates, we find that the estimates by Uenishi & Rice (2004) are applicable to configurations with low background stress and small overstress. None of the published estimates are consistent with numerical results for configurations with high background stress. We therefore derive new equations to estimate the initiation zone size in environments with high background stress. Our results provide guidelines for defining the size of the initiation zone and overstress with minimal effects on the subsequent spontaneous rupture propagation.

Presumed PDF Modeling of Early Flame Propagation in Moderate to Intense Turbulence Environments

NASA Technical Reports Server (NTRS)

Carmen, Christina; Feikema, Douglas A.

2003-01-01

The present paper describes the results obtained from a one-dimensional time dependent numerical technique that simulates early flame propagation in a moderate to intense turbulent environment. Attention is focused on the development of a spark-ignited, premixed, lean methane/air mixture with the unsteady spherical flame propagating in homogeneous and isotropic turbulence. A Monte-Carlo particle tracking method, based upon the method of fractional steps, is utilized to simulate the phenomena represented by a probability density function (PDF) transport equation. Gaussian distributions of fluctuating velocity and fuel concentration are prescribed. Attention is focused on three primary parameters that influence the initial flame kernel growth: the detailed ignition system characteristics, the mixture composition, and the nature of the flow field. The computational results of moderate and intense isotropic turbulence suggests that flames within the distributed reaction zone are not as vulnerable, as traditionally believed, to the adverse effects of increased turbulence intensity. It is also shown that the magnitude of the flame front thickness significantly impacts the turbulent consumption flame speed. Flame conditions studied have fuel equivalence ratio s in the range phi = 0.6 to 0.9 at standard temperature and pressure.

Slow slip pulses driven by thermal pressurization of pore fluid: theory and observational constraints

NASA Astrophysics Data System (ADS)

Garagash, D.

2012-12-01

We discuss recently developed solutions for steadily propagating self-healing slip pulses driven by thermal pressurization (TP) of pore fluid [Garagash, 2012] on a fault with a constant sliding friction. These pulses are characterized by initial stage of undrained weakening of the fault (when fluid/heat can not yet escape the frictionally heated shear zone), which gives way to partial restrengthening due to increasing hydrothermal diffusion under conditions of diminished rate of heating, leading to eventual locking of the slip. The rupture speed of these pulses is decreasing function of the thickness (h) of the principal shear zone. We find that "thick" shear zones, h >> hdyna, where hdyna = (μ/τ0) (ρc/fΛ)(4α/cs), can support aseismic TP pulses propagating at a fraction hdyna/h of the shear wave speed cs, while "thin" shear zones, h˜hdyna or thinner, can only harbor seismic slip. (Here μ - shear modulus, τ0 - the nominal fault strength, f - sliding friction, ρc - the heat capacity of the fault gouge, Λ - the fluid thermal pressurization factor, α - hydrothermal diffusivity parameter of the gouge). For plausible range of fault parameters, hdyna is between 10s to 100s of micrometers, suggesting that slow slip transients propagating at 1 to 10 km/day may occur in the form of a TP slip pulse accommodated by a meter-thick shear zone. We verify that this is, indeed, a possibility by contrasting the predictions for aseismic, small-slip TP pulses operating at seismologically-constrained, near-lithostatic pore pressure (effective normal stress ≈ 3 to 10 MPa) with the observations (slip duration at a given fault location ≈ week, propagation speed ≈ 15 km/day, and the inferred total slip ≈ 2 to 3 cm) for along-strike propagation of the North Cascadia slow slip events of '98-99 [Dragert et al., 2001, 2004]. Furthermore, we show that the effect of thermal pressurization on the strength of the subduction interface is comparable to or exceeds that of the rate-dependence of friction, previously suggested as a mechanism for aseismic transients [e.g., Liu and Rice, 2009; Segall et al., 2010], if the frictional properties of gabbro [He et al., 2007] under the hydrothermal conditions for the North Cascadia slab [Hacker et al., 2003] are used. It therefore appears that while some friction weakening with the slip rate may be required to nucleate a slow slip event in the first place, thermal pressurization mechanism has to be included in realistic models of dynamics of aseismic slip transients, as long as the source of the transients is linked to the conditionally-stable part of the interface (with near velocity-neutral friction). The results of this study point to the importance of the principal shear zone thickness during a slip event and its possible change with the slip rate [e.g., Platt et al., AGU FM 2010]. The insight into how stable creep or a slow slip event may transition into a seismic rupture and how an earthquake rupture "selects" its principal shear zone, which is shown to largely define the TP slip dynamics, may require addressing the slip localization as a phenomena concurrent to the development of transient slip, and therefore coupled to other relevant source mechanisms.

Oceanography and Mine Warfare

DTIC Science & Technology

2000-03-13

of breaking waves , the position and strength of surface currents, and the propagation of the tide into very shallow waters. In the surf zone...6) sediment properties determine shock wave propagation , a method for mine neutralization in the surf zone. 48 OCEANOGRAPHY AND MINE WARFARE...mines will be buried in the sediments, sedimentary explosive shock wave propagation is critical for determining operational performance. Presently, we

Finite-frequency wave propagation through outer rise fault zones and seismic measurements of upper mantle hydration

USGS Publications Warehouse

Miller, Nathaniel; Lizarralde, Daniel

2016-01-01

Effects of serpentine-filled fault zones on seismic wave propagation in the upper mantle at the outer rise of subduction zones are evaluated using acoustic wave propagation models. Modeled wave speeds depend on azimuth, with slowest speeds in the fault-normal direction. Propagation is fastest along faults, but, for fault widths on the order of the seismic wavelength, apparent wave speeds in this direction depend on frequency. For the 5–12 Hz Pn arrivals used in tomographic studies, joint-parallel wavefronts are slowed by joints. This delay can account for the slowing seen in tomographic images of the outer rise upper mantle. At the Middle America Trench, confining serpentine to fault zones, as opposed to a uniform distribution, reduces estimates of bulk upper mantle hydration from ~3.5 wt % to as low as 0.33 wt % H2O.

Propagation analysis of the helicity-drive Alfven wave in the HIST spherical torus plasmas

NASA Astrophysics Data System (ADS)

Hyobu, T.; Hanao, T.; Hirono, H.; Ito, K.; Matsumoto, K.; Nakayama, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2012-10-01

Coaxial Helicity Injection is an efficient current-drive method used in spherical torus experiments. It is a key issue to investigate the dynamo mechanism required to maintain the plasmas. The behavior of a low frequency Alfven wave being possibly related to the dynamo current drive has been studied on HIST. The observed magnetic fluctuation with about 80 kHz propagates along the open flux column (OFC) region, spreading toward the core region. The parallel phase velocity is estimated at 321 km/s from the propagation velocity measured axially along the OFC. The parallel phase velocity agrees well to the Alfven velocity. The radial perpendicular propagation of the Alfven wave can be calculated by a theory based on cold or warm plasma approximation with the Hall term. The theoretical calculation indicates that there are two resonance points and is a cut-off point. These resonance and cut-off points agree well with the magnetic measurement. A part of fluctuation propagates slowly beyond the first resonance point. The wave polarization is left-handed near the resonance point and then converts to be nearly liner outside the resonance point. From these results, we speculate that the torsional Alfven wave evolves to the kinetic Alfven wave during the radial propagation.

Frontal Polymerization in Microgravity: Bubble Behavior and Convection on the KC-135 Aircraft

NASA Technical Reports Server (NTRS)

Pojman, John A.; Ainsworth, William; Chekanov, Yuri; Masere, Jonathan; Volpert, Vitaly; Dumont, Thierry; Wilke, Hermann

2001-01-01

Frontal polymerization is a mode of converting monomer into polymer via a localized exothermic reaction zone that propagates through the coupling of thermal diffusion and Arrhenius reaction kinetics. Frontal polymerization was discovered in Russia by Chechilo and Enikolopyan in 1972. The macrokinetics and dynamics of frontal polymerization have been examined in detail and applications for materials synthesis considered. Large temperature and concentration gradients that occur in the front lead to large density gradients. A schematic is presented for a liquid monomer, usually a monoacrylate, being converted to a liquid (thermoplastic) polymer. The velocity can be controlled by the initiator concentration but is on the order of a cm/min. If the liquid monomer is multifunctional, then a solid (thermoset) polymer is formed. Convection can occur with all types of monomers if the front propagates up a tube. Bowden et al. studied liquid/solid systems. McCaughey et al. studied liquid polymer systems. Descending fronts in thermoplastic systems are also susceptible to the Rayleigh-Taylor instability.

Imaging The Shallow Velocity Structure Of The Hikurangi Megathrust Using Full-Waveform Inversion

NASA Astrophysics Data System (ADS)

Gray, M.; Bell, R. E.; Morgan, J. V.

2017-12-01

The Hikurangi margin, offshore North Island, New Zealand, exhibits a number of different slip behaviours, including shallow slow slip events (SSEs) (<2km to 15 km). There is also a strong contrast in geodetic coupling along the margin. While reflection data provides an image of the structure, no information about physical properties is provided. Full-waveform inversion (FWI) is an imaging technique which incorporates the full seismic wavelet rather than just the first arrivals, as in traditional tomography. By propagating synthetic seismic waves through a velocity model and comparing the synthetic wavelets to the field data, we update the velocity model until the real and synthetic wavelets match. In this way, we can resolve high-resolution physical property variations which influence the seismic wavefield. In our study, FWI was used to resolve the P-wave velocity structure at the Hikurangi megathrust up to 2km. This method enables investigation of how upper-plate structure may influence plate boundary slip behaviour. In 2005, a seismic survey was carried out over the Hikurangi megathrust. The data was acquired from a 12km streamer, allowing FWI analysis up to 2km below the seabed. The results show low velocity zones correlating to faults interpreted from reflection seismic imaging. We believe these low velocity zones, particularly near the frontal thrust resolve faulting in the area, and present these faults as possible fluid conduits. As the dataset was not collected specifically for FWI, the results show promise in resolving more information at depth. As such, both a 3D seismic survey and two drilling expeditions have been approved for the period November 2017 - May 2018. The seismic survey will be carried out with parameters optimal for FWI, allow imaging of the fault boundary, which is not possible with the current 2D data. The cores will provide direct geological evidence which can be used in conjunction with velocity models to discern lithology and structure. The current result identifies the existence of overpressure and aids in drilling safety when collecting these cores. In conjunction with the new IODP cores, the FWI model will improve understanding of properties of the shallow structure of the megathrust.

Effects of equivalence ratio variation on lean, stratified methane-air laminar counterflow flames

NASA Astrophysics Data System (ADS)

Richardson, E. S.; Granet, V. E.; Eyssartier, A.; Chen, J. H.

2010-11-01

The effects of equivalence ratio variations on flame structure and propagation have been studied computationally. Equivalence ratio stratification is a key technology for advanced low emission combustors. Laminar counterflow simulations of lean methane-air combustion have been presented which show the effect of strain variations on flames stabilized in an equivalence ratio gradient, and the response of flames propagating into a mixture with a time-varying equivalence ratio. 'Back supported' lean flames, whose products are closer to stoichiometry than their reactants, display increased propagation velocities and reduced thickness compared with flames where the reactants are richer than the products. The radical concentrations in the vicinity of the flame are modified by the effect of an equivalence ratio gradient on the temperature profile and thermal dissociation. Analysis of steady flames stabilized in an equivalence ratio gradient demonstrates that the radical flux through the flame, and the modified radical concentrations in the reaction zone, contribute to the modified propagation speed and thickness of stratified flames. The modified concentrations of radical species in stratified flames mean that, in general, the reaction rate is not accurately parametrized by progress variable and equivalence ratio alone. A definition of stratified flame propagation based upon the displacement speed of a mixture fraction dependent progress variable was seen to be suitable for stratified combustion. The response times of the reaction, diffusion, and cross-dissipation components which contribute to this displacement speed have been used to explain flame response to stratification and unsteady fluid dynamic strain.

Azimuthally Anisotropic 3D Velocity Continuation

DOE PAGES

Burnett, William; Fomel, Sergey

2011-01-01

We extend time-domain velocity continuation to the zero-offset 3D azimuthally anisotropic case. Velocity continuation describes how a seismic image changes given a change in migration velocity. This description turns out to be of a wave propagation process, in which images change along a velocity axis. In the anisotropic case, the velocity model is multiparameter. Therefore, anisotropic image propagation is multidimensional. We use a three-parameter slowness model, which is related to azimuthal variations in velocity, as well as their principal directions. This information is useful for fracture and reservoir characterization from seismic data. We provide synthetic diffraction imaging examples to illustratemore » the concept and potential applications of azimuthal velocity continuation and to analyze the impulse response of the 3D velocity continuation operator.« less

Laboratory model of the cardiovascular system for experimental demonstration of pulse wave propagation

NASA Astrophysics Data System (ADS)

Stojadinović, Bojana; Nestorović, Zorica; Djurić, Biljana; Tenne, Tamar; Zikich, Dragoslav; Žikić, Dejan

2017-03-01

The velocity by which a disturbance moves through the medium is the wave velocity. Pulse wave velocity is among the key parameters in hemodynamics. Investigation of wave propagation through the fluid-filled elastic tube has a great importance for the proper biophysical understanding of the nature of blood flow through the cardiovascular system. Here, we present a laboratory model of the cardiovascular system. We have designed an experimental setup which can help medical and nursing students to properly learn and understand basic fluid hemodynamic principles, pulse wave and the phenomenon of wave propagation in blood vessels. Demonstration of wave propagation allowed a real time observation of the formation of compression and expansion waves by students, thus enabling them to better understand the difference between the two waves, and also to measure the pulse wave velocity for different fluid viscosities. The laboratory model of the cardiovascular system could be useful as an active learning methodology and a complementary tool for understanding basic principles of hemodynamics.

Peak Stress Intensity Factor Governs Crack Propagation Velocity In Crosslinked UHMWPE

PubMed Central

Sirimamilla, P. Abhiram; Furmanski, Jevan; Rimnac, Clare

2013-01-01

Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax-Kmin, MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax, during cyclic loading, rather than by ΔK. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components. PMID:23165898

Bubble propagation in a pipe filled with sand.

PubMed

Gendron, D; Troadec, H; Måløy, K J; Flekkøy, E G

2001-08-01

Granular flow with strong hydrodynamic interactions has been studied experimentally. Experiments have been carried out to study the movement of a single bubble in an inclined tube filled with glass beads and air. A maximum bubble velocity was found at an inclined angle straight theta(m). The density variations in the sand were measured by capacitance measurements, and a decompactification zone was observed just above the bubble when the inclination angle straight theta was larger than straight theta(m). The length of the decompactification front increased with increasing inclination angle and disappeared for angles smaller than straight theta(m). Both pressure and visualization experiments were carried out and compared with the density measurements.

Ultrasonic probing of the fracture process zone in rock using surface waves

NASA Technical Reports Server (NTRS)

Swanson, P. L.; Spetzler, H.

1984-01-01

A microcrack process zone is frequently suggested to accompany macrofractures in rock and play an important role in the resistance to fracture propagation. Attenuation of surface waves propagating through mode I fractures in wedge-loaded double-cantilever beam specimens of Westerly granite has been recorded in an attempt to characterize the structure of the fracture process zone. The ultrasonic measurements do not support the generally accepted model of a macroscopic fracture that incrementally propagates with the accompaniment of a cloud of microcracks. Instead, fractures in Westerly granite appear to form as gradually separating surfaces within a zone having a width of a few millimeters and a length of several tens of millimeters. A fracture process zone of this size would necessitate the use of meter-sized specimens in order for linear elastic fracture mechanics to be applicable.

Dynamic earthquake rupture simulations on nonplanar faults embedded in 3D geometrically complex, heterogeneous elastic solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duru, Kenneth, E-mail: kduru@stanford.edu; Dunham, Eric M.; Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA

Dynamic propagation of shear ruptures on a frictional interface in an elastic solid is a useful idealization of natural earthquakes. The conditions relating discontinuities in particle velocities across fault zones and tractions acting on the fault are often expressed as nonlinear friction laws. The corresponding initial boundary value problems are both numerically and computationally challenging. In addition, seismic waves generated by earthquake ruptures must be propagated for many wavelengths away from the fault. Therefore, reliable and efficient numerical simulations require both provably stable and high order accurate numerical methods. We present a high order accurate finite difference method for: a)more » enforcing nonlinear friction laws, in a consistent and provably stable manner, suitable for efficient explicit time integration; b) dynamic propagation of earthquake ruptures along nonplanar faults; and c) accurate propagation of seismic waves in heterogeneous media with free surface topography. We solve the first order form of the 3D elastic wave equation on a boundary-conforming curvilinear mesh, in terms of particle velocities and stresses that are collocated in space and time, using summation-by-parts (SBP) finite difference operators in space. Boundary and interface conditions are imposed weakly using penalties. By deriving semi-discrete energy estimates analogous to the continuous energy estimates we prove numerical stability. The finite difference stencils used in this paper are sixth order accurate in the interior and third order accurate close to the boundaries. However, the method is applicable to any spatial operator with a diagonal norm satisfying the SBP property. Time stepping is performed with a 4th order accurate explicit low storage Runge–Kutta scheme, thus yielding a globally fourth order accurate method in both space and time. We show numerical simulations on band limited self-similar fractal faults revealing the complexity of rupture dynamics on rough faults.« less

Dynamic earthquake rupture simulations on nonplanar faults embedded in 3D geometrically complex, heterogeneous elastic solids

NASA Astrophysics Data System (ADS)

Duru, Kenneth; Dunham, Eric M.

2016-01-01

Dynamic propagation of shear ruptures on a frictional interface in an elastic solid is a useful idealization of natural earthquakes. The conditions relating discontinuities in particle velocities across fault zones and tractions acting on the fault are often expressed as nonlinear friction laws. The corresponding initial boundary value problems are both numerically and computationally challenging. In addition, seismic waves generated by earthquake ruptures must be propagated for many wavelengths away from the fault. Therefore, reliable and efficient numerical simulations require both provably stable and high order accurate numerical methods. We present a high order accurate finite difference method for: a) enforcing nonlinear friction laws, in a consistent and provably stable manner, suitable for efficient explicit time integration; b) dynamic propagation of earthquake ruptures along nonplanar faults; and c) accurate propagation of seismic waves in heterogeneous media with free surface topography. We solve the first order form of the 3D elastic wave equation on a boundary-conforming curvilinear mesh, in terms of particle velocities and stresses that are collocated in space and time, using summation-by-parts (SBP) finite difference operators in space. Boundary and interface conditions are imposed weakly using penalties. By deriving semi-discrete energy estimates analogous to the continuous energy estimates we prove numerical stability. The finite difference stencils used in this paper are sixth order accurate in the interior and third order accurate close to the boundaries. However, the method is applicable to any spatial operator with a diagonal norm satisfying the SBP property. Time stepping is performed with a 4th order accurate explicit low storage Runge-Kutta scheme, thus yielding a globally fourth order accurate method in both space and time. We show numerical simulations on band limited self-similar fractal faults revealing the complexity of rupture dynamics on rough faults.

Position Estimation Method of Medical Implanted Devices Using Estimation of Propagation Velocity inside Human Body

NASA Astrophysics Data System (ADS)

Kawasaki, Makoto; Kohno, Ryuji

Wireless communication devices in the field of medical implant, such as cardiac pacemakers and capsule endoscopes, have been studied and developed to improve healthcare systems. Especially it is very important to know the range and position of each device because it will contribute to an optimization of the transmission power. We adopt the time-based approach of position estimation using ultra wideband signals. However, the propagation velocity inside the human body differs in each tissue and each frequency. Furthermore, the human body is formed of various tissues with complex structures. For this reason, propagation velocity is different at a different point inside human body and the received signal so distorted through the channel inside human body. In this paper, we apply an adaptive template synthesis method in multipath channel for calculate the propagation time accurately based on the output of the correlator between the transmitter and the receiver. Furthermore, we propose a position estimation method using an estimation of the propagation velocity inside the human body. In addition, we show by computer simulation that the proposal method can perform accurate positioning with a size of medical implanted devices such as a medicine capsule.

Constraints on Shallow Crustal Structure across the San Andreas Fault Zone, Coachella Valley, Southern California: Results from the Salton Seismic Imaging Project (SSIP)

NASA Astrophysics Data System (ADS)

Hernandez, A.; Persaud, P.; Bauer, K.; Stock, J. M.; Fuis, G. S.; Hole, J. A.; Goldman, M.

2015-12-01

The strong influence of basin structure and crustal heterogeneities on seismic wave propagation suggests that these factors should be included in calculations of strong ground shaking. Knowledge of the shallow subsurface is thus essential for an accurate seismic hazard estimate for the densely populated Coachella Valley, the region north of the potential M7.8 rupture near the Salton Sea. Using SSIP data, we analyzed first arrivals from nine 65-911 kg explosive shots recorded along a profile in the Coachella Valley in order to evaluate the interpretation of our 2D tomographic results and give added details on the structural complexity of the shallow crust. The line extends 37 km from the Peninsular Ranges to the Little San Bernardino Mountains crossing the major strands of the San Andreas Fault Zone. We fit traveltime curves to our picks with forward modeling ray tracing, and determined 1D P-wave velocity models for traveltime arrivals east and west of each shot, and a 2D model for the line. We also inferred the geometry of near-vertical faults from the pre-stack line migration method of Bauer et al. (2013). In general, the 1D models east of individual shots have deeper basement contacts and lower apparent velocities, ~5 km/s at 4 km depth, whereas the models west of individual shots have shallower basement and velocities up to 6 km/s at 2 km depth. Mismatches in basement depths (assuming 5-6 km/s) between individual 1D models indicate a shallowly dipping basement, deepening eastward towards the Banning Fault and shoaling abruptly farther east. An east-dipping structure in the 2D model also gives a better fit than horizontal layers. Based on high velocity zones derived from traveltimes at 9-20 km from the western end of the line, we included an offset from ~2 km to 4 km depth near the middle of the line, which significantly improved the 2D model fit. If fault-related, this offset could represent the Garnet Hill Fault if it continues southward in the subsurface.

Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion Data in the Wavelet Domain Constrained by Sparsity Regularization

NASA Astrophysics Data System (ADS)

Zhang, H.; Fang, H.; Yao, H.; Maceira, M.; van der Hilst, R. D.

2014-12-01

Recently, Zhang et al. (2014, Pure and Appiled Geophysics) have developed a joint inversion code incorporating body-wave arrival times and surface-wave dispersion data. The joint inversion code was based on the regional-scale version of the double-difference tomography algorithm tomoDD. The surface-wave inversion part uses the propagator matrix solver in the algorithm DISPER80 (Saito, 1988) for forward calculation of dispersion curves from layered velocity models and the related sensitivities. The application of the joint inversion code to the SAFOD site in central California shows that the fault structure is better imaged in the new model, which is able to fit both the body-wave and surface-wave observations adequately. Here we present a new joint inversion method that solves the model in the wavelet domain constrained by sparsity regularization. Compared to the previous method, it has the following advantages: (1) The method is both data- and model-adaptive. For the velocity model, it can be represented by different wavelet coefficients at different scales, which are generally sparse. By constraining the model wavelet coefficients to be sparse, the inversion in the wavelet domain can inherently adapt to the data distribution so that the model has higher spatial resolution in the good data coverage zone. Fang and Zhang (2014, Geophysical Journal International) have showed the superior performance of the wavelet-based double-difference seismic tomography method compared to the conventional method. (2) For the surface wave inversion, the joint inversion code takes advantage of the recent development of direct inversion of surface wave dispersion data for 3-D variations of shear wave velocity without the intermediate step of phase or group velocity maps (Fang et al., 2014, Geophysical Journal International). A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. We will test the new joint inversion code at the SAFOD site to compare its performance over the previous code. We will also select another fault zone such as the San Jacinto Fault Zone to better image its structure.

Nature and Role of Subducting Sediments on the Megathrust and Forearc Evolution in the 2004 Great Sumatra Earthquake Rupture Zone: Results from Full Waveform Inversion of Long Offset Seismic Data

NASA Astrophysics Data System (ADS)

Singh, S. C.; Qin, Y.

2015-12-01

On active accretionary margins, the nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Drilling is the most direct method to characterise the nature of these sediments, but the drilling is very expensive, and provide information at only a few locations. In north Sumatra, an IODP drilling is programmed to take place in July-August 2016. We have performed seismic full waveform inversion of 12 km long offset seismic reflection data acquired by WesternGeco in 2006 over a 35 km zone near the subduction front in the 2004 earthquake rupture zone area that provide detailed quantitative information on the characteristics of the incoming sediments. We first downward continue the surface streamer data to the seafloor, which removes the effect of deep water (~5 km) and brings out the refraction arrivals as the first arrivals. We carry out travel time tomography, and then performed full waveform inversion of seismic refraction data followed by the full waveform inversion of reflection data providing detailed (10-20 m) velocity structure. The sediments in this area are 3-5 km thick where the P-wave velocity increases from 1.6 km/s near the seafloor to more than 4.5 km/s above the oceanic crust. The high velocity of sediments above the basement suggests that the sediments are highly compacted, strengthened the coupling near the subduction front, which might have been responsible for 2004 earthquake rupture propagation up to the subduction front, enhancing the tsunami. We also find several thin velocity layers within the sediments, which might be due to high pore-pressure fluid or free gas. These layers might be responsible for the formation of pseudo-decollement within the forearc sediments that acts as a conveyer belt between highly compacted subducting lower sediments and accreted sediments above. The presence of well intact sediments on the accretionary prism supports this interpretation. Our results provide first hand information about the sediments properties, which will be ground toothed by drilling.

Influence of the osteosynthesis plate on ultrasound propagation in the bone

PubMed Central

Bezuti, Márcio Takey; Mandarano-Filho, Luiz Garcia; Barbieri, Giuliano; Mazzer, Nilton; Barbieri, Cláudio Henrique

2014-01-01

Objective: To analyze the influence of steel plates for osteosynthesis on the velocity of ultrasound propagation (VU) through the bone. Methods: The transverse coronal and sagittal velocity of ultrasound propagation underwater were measured on the intact bone and then on assemblies of the same bone with two types of osteosynthesis plates (DCP and semi tubular), fixed onto the dorsal side of the bones. The first arriving signal (FAS) was the ultrasound parameter used, taking the coronal and sagittal diameters as the distances to calculate velocity. Intergroup statistical comparisons were made at significance level of 1% (p<0.01). Results: Velocity was higher on the intact bones than on the bone-plate assemblies and higher for the semitubular than for the compression plates, although differences were not statistically significant for most comparisons (p=0.0132 to 0.9884), indicating that the steel plates do not interfere significantly with ultrasound wave propagation through the bone-plate assemblies. Conclusion: The velocity reduction effect was attributed to the greater reflection coefficient of the steel as compared to that of bone and water. Ultrasonometry can, thus, be used in the evaluation of healing of fractures fixed with steel plates. Experimental Study. PMID:25328436

Subsurface imaging of grain microstructure using picosecond ultrasonics

DOE PAGES

Khafizov, M.; Pakarinen, J.; He, L.; ...

2016-04-21

We report on imaging subsurface grain microstructure using picosecond ultrasonics. This approach relies on elastic anisotropy of crystalline materials where ultrasonic velocity depends on propagation direction relative to the crystal axes. Picosecond duration ultrasonic pulses are generated and detected using ultrashort light pulses. In materials that are transparent or semitransparent to the probe wavelength, the probe monitors GHz Brillouin oscillations. The frequency of these oscillations is related to the ultrasonic velocity and the optical index of refraction. Ultrasonic waves propagating across a grain boundary experience a change in velocity due to a change in crystallographic orientation relative to the ultrasonicmore » propagation direction. This change in velocity is manifested as a change in the Brillouin oscillation frequency. Using the ultrasonic propagation velocity, the depth of the interface can be determined from the location in time of the transition in oscillation frequency. An image of the grain boundary is obtained by scanning the beam along the surface. We demonstrate this volumetric imaging capability using a polycrystalline UO 2 sample. As a result, cross section liftout analysis of the grain boundaries using electron microscopy were used to verify our imaging results.« less

Atomistic Simulations of Detonation Instabilities in Condensed Phase Systems

NASA Astrophysics Data System (ADS)

Kober, Edward; Heim, Andrew; Germann, Timothy; Jensen, Niels

2007-06-01

We report the results of simulations of condensed phase detonation phenomena using a model diatomic system: 2AB -> A2 + B2. The initial set of parameters for this system corresponded to the Model 0 set of C. White et al, which exhibits a steady, Chapman-Jouget (CJ) detonation structure with a reaction zone length of 30-100 å. This has a highly compressed CJ state (V/V0˜0.5) that does not consist of discrete molecular species. The potential form was modified so that a more molecular CJ state resulted, consistent with the models for conventional organic explosives. The new system has a less dense CJ state (V/V0˜0.8), and the reaction zone was substantially extended. The reaction rate fits Arrhenius-type kinetics with an activation energy of ˜2 eV, with a minor density dependence. In contrast, the original Model 0 system had a lower activation energy (˜1 eV) with a stronger density dependence. The new system exhibits quite marked two dimensional instability structures with well-defined wavelengths similar to what has been observed for gas-phase detonations and for nitromethane. Depending on the exothermicity and the width of the periodic simulations, these instabilities can result in either detonation failure or quasi-steady propagation. The observed propagation velocities are several per cent higher than CJ values derived from thermodynamic analyses.

Macro-Scale Reactive Flow Model for High-Explosive Detonation in Support of ASCI Weapon Safety Milepost

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reaugh, J E

2002-01-03

Explosive grain-scale simulations are not practical for weapon safety simulations. Indeed for nearly ideal explosives with reaction zones of order 500 {micro}m, even reactive flow models are not practical for weapon safety simulations. By design, reactive flow models must resolve the reaction zone, which implies computational cells with dimension of order 50 {micro}m for such explosives. The desired result for a simulation in which the reaction zone is not resolved is that the explosive behaves as an ideal one. The pressure at the shock front rises to the Chapman-Jouget (CJ) pressure with a reaction zone dimension that is like thatmore » of a shock propagating in an unreactive medium, on the order of a few computational cells. It should propagate with the detonation velocity that is determined by the equation of state of the products. In the past, this was achieved in one dimensional simulations with ''beta-burn'', a method in which the extent of conversion to final product is proportional to the approach of the specific volume in the shock front to the specific volume of the CJ state. One drawback with this method is that there is a relatively long build-up to steady detonation that is typically 50 to 100 computational cells. The need for relatively coarsely zoned simulations in two dimensions lead to ''program-burn'' by which the time to detonation can be determined by a simple ray-tracing algorithm when there are no barriers or shadows. Complications arise in two and three dimensions to the extent that some calculations of the lighting time in complex geometry can give incorrect results. We sought to develop a model based on reactive flow that might help the needs of the Weapon Safety Simulation milepost. Important features of the model are: (1) That it be useable with any equation of state description of the explosive product gases including both JWL and LEOS table forms. (2) That it exhibits the desired dependence on zone size. We believe that the model described here does exhibit these features.« less

Mitigation of cross-beam energy transfer: Implication of two-state focal zooming on OMEGA

NASA Astrophysics Data System (ADS)

Froula, D. H.; Kessler, T. J.; Igumenshchev, I. V.; Betti, R.; Goncharov, V. N.; Huang, H.; Hu, S. X.; Hill, E.; Kelly, J. H.; Meyerhofer, D. D.; Shvydky, A.; Zuegel, J. D.

2013-08-01

Cross-beam energy transfer (CBET) during OMEGA low-adiabat cryogenic experiments reduces the hydrodynamic efficiency by ˜35%, which lowers the calculated one-dimensional (1-D) yield by a factor of 7. CBET can be mitigated by reducing the diameter of the laser beams relative to the target diameter. Reducing the diameter of the laser beams by 30%, after a sufficient conduction zone has been generated (two-state zooming), is predicted to maintain low-mode uniformity while recovering 90% of the kinetic energy lost to CBET. A radially varying phase plate is proposed to implement two-state zooming on OMEGA. A beam propagating through the central half-diameter of the phase plate will produce a large spot, while a beam propagating through the outer annular region of the phase plate will produce a narrower spot. To generate the required two-state near-field laser-beam profile, a picket driver with smoothing by spectral dispersion (SSD) would pass through an apodizer, forming a beam of half the standard diameter. A second main-pulse driver would co-propagate without SSD through its own apodizer, forming a full-diameter annular beam. Hydrodynamic simulations, using the designed laser spots produced by the proposed zooming scheme on OMEGA, show that implementing zooming will increase the implosion velocity by 25% resulting in a 4.5× increase in the 1-D neutron yield. Demonstrating zooming on OMEGA would validate a viable direct-drive CBET mitigation scheme and help establish a pathway to hydrodynamically equivalent direct-drive-ignition implosions by increasing the ablation pressure (1.6×), which will allow for more stable implosions at ignition-relevant velocities.

Normal impact of a low-velocity projectile against a taut string-like membrane

NASA Astrophysics Data System (ADS)

Zhao, Yifei; Sun, Zhili

2018-07-01

For the impact system in which a moving projectile transversely impacts against a taut fabric band, 1-D linearized model applies because of low-velocity, sufficient pretension, and the sizes of the objects. This projectile-to-band impact model can serve as the physical prototype of applications in engineering such as cable-membrane architectures and seat belts. In this fundamental work, the response properties under central and non-central impacts are investigated analytically from the viewpoint of wave propagations, while comparisons and verifications are made with finite element (FE) analysis. For a central impact after the first separation, band can catch up with the projectile such that a contact-impact state is re-established when m is in the small interval neighbouring m = 1. For a non-central impact, the projectile would be subjected to a combination of translation and rotation due to asymmetric wave propagations. From every certain instant, the projectile is subjected to an additional rotational acceleration (principal moment) with an abrupt or zero initial value in the anti-clockwise or clockwise direction. The swing amplitude of a small-j or a flat projectile is susceptible to significant fluctuations, and vice versa. The band with a rather large off-centre ratio for the impacted zone and a rather short length of the shorter segment would facilitate a larger accumulation of swing amplitude in a single direction soon after the impact. The linearized impact models proposed can be used to well describe the small-deflection responses for the system, based on 1-D wave propagations or the dependence of quasi-static band deflection on time if the impact duration is much longer than the double wave transit time for the band.

Kink-bands: Shock deformation of biotite resulting from a nuclear explosion

USGS Publications Warehouse

Cummings, D.

1965-01-01

Microscopic examination of granodiorite samples from the shock region around a nuclear explosion reveals sharply folded lens-shaped zones (kink-bands) in the mineral biotite. Fifty percent of these zones are oriented approximately 90?? to the direction of shock-wave propagation, but other zones are symmetrically concentrated at shear angles of 50?? and 70?? to the direction of shock-wave propagation.

Subcontinental-scale crustal velocity changes along the Pacific-North America plate boundary.

PubMed

Davis, J L; Wernicke, B P; Bisnath, S; Niemi, N A; Elósegui, P

2006-06-29

Transient tectonic deformation has long been noted within approximately 100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (approximately 1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse approximately 1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific-North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by approximately 1 mm yr(-1) starting in late 1999.

Detonation propagation in a high loss configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Scott I; Shepherd, Joseph E

2009-01-01

This work presents an experimental study of detonation wave propagation in tubes with inner diameters (ID) comparable to the mixture cell size. Propane-oxygen mixtures were used in two test section tubes with inner diameters of 1.27 mm and 6.35 mm. For both test sections, the initial pressure of stoichiometric mixtures was varied to determine the effect on detonation propagation. For the 6.35 mm tube, the equivalence ratio {phi} (where the mixture was {phi} C{sub 3}H{sub 8} + 50{sub 2}) was also varied. Detonations were found to propagate in mixtures with cell sizes as large as five times the diameter ofmore » the tube. However, under these conditions, significant losses were observed, resulting in wave propagation velocities as slow as 40% of the CJ velocity U{sub CJ}. A review of relevant literature is presented, followed by experimental details and data. Observed velocity deficits are predicted using models that account for boundary layer growth inside detonation waves.« less

Notch-Boosted Domain Wall Propagation in Magnetic Nanowires

NASA Astrophysics Data System (ADS)

Wang, Xiang Rong; Yuan, Hauiyang

Magnetic domain wall (DW) motion along a nanowire underpins many proposals of spintronic devices. High DW propagation velocity is obviously important because it determines the device speed. Thus it is interesting to search for effective control knobs of DW dynamics. We report a counter-intuitive finding that notches in an otherwise homogeneous magnetic nanowire can boost current-induced domain wall (DW) propagation. DW motion in notch-modulated wires can be classified into three phases: 1) A DW is pinned around a notch when the current density is below the depinning current density. 2) DW propagation velocity above the depinning current density is boosted by notches when non-adiabatic spin-transfer torque strength is smaller than the Gilbert damping constant. The boost can be many-fold. 3) DW propagation velocity is hindered when non-adiabatic spin-transfer torque strength is larger than the Gilbert damping constant. This work was supported by Hong Kong GRF Grants (Nos. 163011151 and 605413) and the Grant from NNSF of China (No. 11374249).

Deceleration efficiencies of shrub windbreaks in a wind tunnel

NASA Astrophysics Data System (ADS)

Wu, Xiaoxu; Zou, Xueyong; Zhou, Na; Zhang, Chunlai; Shi, Sha

2015-03-01

Artemisia and Salix are dominant shrub species for windbreaks in arid areas of China, and they show similar features to shrubs in other arid areas of the world. We compared the mean velocity fields and shelter effects of two shrub windbreaks with different layouts. For a single plant of Artemisia, the higher the free airflow velocity is, the more the wind velocity around two sides of the plant increases. The velocity gradient around a single plant of Salix is smaller than that around an Artemisia plant due to the difference in the plant shapes. Seven new velocity zones in the horizontal direction appear when airflow passes through an Artemisia windbreak, including four deceleration zones and three acceleration zones. The mean velocity field that is affected by a Salix windbreak can be divided into a deceleration zone in the front, an acceleration zone above, a vortex zone behind and a restoration zone downwind of the vortex zone. Shelter effects of the shrub windbreaks vary with the wind velocity and are influenced by the construct of the windbreaks. Shrub windbreaks that have a complex construction have better shelter effects than simple ones. The shelter effects of plant windbreaks are also influenced by the growth features of the plants. Considering the plant characteristics and the shelter effects of Salix and Artemisia windbreaks, it is optimal to plant these two windbreaks together in a sand-control system. This research is intended to be useful for sand movement control in arid areas.

Spectral modification of seismic waves propagating through solids exhibiting a resonance frequency: a 1-D coupled wave propagation-oscillation model

NASA Astrophysics Data System (ADS)

Frehner, Marcel; Schmalholz, Stefan M.; Podladchikov, Yuri

2009-02-01

A 1-D model is presented that couples the microscale oscillations of non-wetting fluid blobs in a partially saturated poroelastic medium with the macroscale wave propagation through the elastic skeleton. The fluid oscillations are caused by surface tension forces that act as the restoring forces driving the oscillations. The oscillations are described mathematically with the equation for a linear oscillator and the wave propagation is described with the 1-D elastic wave equation. Coupling is done using Hamilton's variational principle for continuous systems. The resulting linear system of two partial differential equations is solved numerically with explicit finite differences. Numerical simulations are used to analyse the effect of solids exhibiting internal oscillations, and consequently a resonance frequency, on seismic waves propagating through such media. The phase velocity dispersion relation shows a higher phase velocity in the high-frequency limit and a lower phase velocity in the low-frequency limit. At the resonance frequency a singularity in the dispersion relation occurs. Seismic waves can initiate oscillations of the fluid by transferring energy from solid to fluid at the resonance frequency. Due to this transfer, the spectral amplitude of the solid particle velocity decreases at the resonance frequency. After initiation, the oscillatory movement of the fluid continuously transfers energy at the resonance frequency back to the solid. Therefore, the spectral amplitude of the solid particle velocity is increased at the resonance frequency. Once initiated, fluid oscillations decrease in amplitude with increasing time. Consequently, the spectral peak of the solid particle velocity at the resonance frequency decreases with time.

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

NASA Astrophysics Data System (ADS)

Hasegawa, Akira; Nakajima, Junichi

2017-12-01

We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H2O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration-derived H2O causes intermediate-depth intraslab earthquakes. However, it is possible that dual mechanisms generate these earthquakes; the initiation of earthquake rupture may be caused by local excess pore pressure from H2O, and subsequent ruptures may propagate through thermal shear instability. In either case, slab-derived H2O plays an important role in generating intermediate-depth events.

Observations and a model of undertow over the inner continental shelf

USGS Publications Warehouse

Lentz, Steven J.; Fewings, Melanie; Howd, Peter; Fredericks, Janet; Hathaway, Kent

2008-01-01

Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth.During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1–6 cm s−1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf “Hasselmann wave stress” due to the influence of the earth’s rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.

The structure of premixed particle-cloud flames

NASA Technical Reports Server (NTRS)

Seshadri, K.; Berlad, A. L.; Tangirala, V.

1992-01-01

The structure of premixed flames propagating in combustible systems, containing uniformly distributed volatile fuel particles, in an oxidizing gas mixture, is analyzed. It is presumed that the fuel particles vaporize first to yield a gaseous fuel of known chemical structure, which is subsequently oxidized in the gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number, based on the gas-phase oxidation of the gaseous fuel is large, and for values of phi(u) greater than or equal to 1.0, where phi(u) is the equivalence ratio based on the fuel available in the fuel particles. The structure of the flame is presumed to consist of a preheat vaporization zone where the rate of the gas-phase chemical reaction is small, a reaction zone where convection and the rate of vaporization of the fuel particles are small and a convection zone where diffusive terms in the conservation equations are small. For given values phi(u) the analysis yields results for the burning velocity and phi(g) where phi(g) is the effective equivalence ratio in the reaction zone. The analysis shows that even though phi(u) greater than or equal to 1.0, for certain cases the calculated value of phi(g) is less than unity. This prediction is in agreement with experimental observations.

Fault zone property near Xinfengjiang Reservoir using dense, across-fault seismic array

NASA Astrophysics Data System (ADS)

Lee, M. H. B.; Yang, H.; Sun, X.

2017-12-01

Properties of fault zones are important to the understanding of earthquake process. Around the fault zone is a damaged zone which is characterised by a lower seismic velocity. This is detectable as a low velocity zone and measure some physical property of the fault zone, which is otherwise difficult sample directly. A dense, across-fault array of short period seismometer is deployed on an inactive fault near Xinfengjiang Reservoir. Local events were manually picked. By computing the synthetic arrival time, we were able to constrain the parameters of the fault zone Preliminary result shows that the fault zone is around 350 m wide with a P and S velocity increase of around 10%. The fault is geologically inferred, and this result suggested that it may be a geological layer. The other possibility is that the higher velocity is caused by a combination of fault zone healing and fluid intrusion. Whilst the result was not able to tell us the nature of the fault, it demonstrated that this method is able to derive properties from a fault zone.

Azimuthal propagation of storm time Pc 5 waves observed simultaneously by geostationary satellites GOES 2 and GOES 3

NASA Astrophysics Data System (ADS)

Lin, C. S.; Barfield, J. N.

1985-11-01

Storm-time Pc 5 wave events observed simultaneously by the GOES 2 and GOES 3 satellites in the afternoon sector during the 1-year interval of March 1979 to February 1980 are surveyed to learn the wave propagation. Essentially, all storm-time Pc 5 waves (approximately 93 percent) are found to propagate westward azimuthally with a velocity of 5 to 50 km/s and a wavelength of 1000 km to 9000 km (Only two of 30 events had eastward propagation, with a velocity of about 150 km/s). It is concluded that westward propagating waves are excited by ion drift instabilities associated with the ion ring current, and that the eastward propagating waves are excited by surface waves on the magnetopause through Kelvin-Helmholtz instability.

The Iceland Plate Boundary Zone: Propagating Rifts, Migrating Transforms, and Rift-Parallel Strike-Slip Faults

NASA Astrophysics Data System (ADS)

Karson, J. A.

2017-11-01

Unlike most of the Mid-Atlantic Ridge, the North America/Eurasia plate boundary in Iceland lies above sea level where magmatic and tectonic processes can be directly investigated in subaerial exposures. Accordingly, geologic processes in Iceland have long been recognized as possible analogs for seafloor spreading in the submerged parts of the mid-ocean ridge system. Combining existing and new data from across Iceland provides an integrated view of this active, mostly subaerial plate boundary. The broad Iceland plate boundary zone includes segmented rift zones linked by transform fault zones. Rift propagation and transform fault migration away from the Iceland hotspot rearrange the plate boundary configuration resulting in widespread deformation of older crust and reactivation of spreading-related structures. Rift propagation results in block rotations that are accommodated by widespread, rift-parallel, strike-slip faulting. The geometry and kinematics of faulting in Iceland may have implications for spreading processes elsewhere on the mid-ocean ridge system where rift propagation and transform migration occur.

Conditions for the existence of Kelvin-Helmholtz instability in a CME

NASA Astrophysics Data System (ADS)

Jatenco-Pereira, Vera; Páez, Andrés; Falceta-Gonçalves, Diego; Opher, Merav

2015-08-01

The presence of Kelvin-Helmholtz instability (KHI) in the sheaths of the Coronal Mass Ejection (CME) has motivated several analysis and simulations to test their existence. In the present work we assume the existence of the KHI and propose a method to identify the regions where it is possible the development of KHI for a CME propagating in a fast and slow solar wind. We build functions for the velocities, densities and magnetic fields for two different zones of interaction between the solar wind and a CME. Based on the theory of magnetic KHI proposed by Chandrasekhar (1961) and we found conditions for the existence of KHI in the CME sheaths. Using this method it is possible to determine the range of parameters, in particular CME magnetic fields in which the KHI could exist. We conclude that KHI may exist in the two CME flanks and it is perceived that the zone with boundaries with the slow solar wind is more appropriated for the formation of the KHI.

Studies of supersonic, radiative plasma jet interaction with gases at the Prague Asterix Laser System facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nicolaie, Ph.; Stenz, C.; Tikhonchuk, V.

2008-08-15

The interaction of laser driven jets with gas puffs at various pressures is investigated experimentally and is analyzed by means of numerical tools. In the experiment, a combination of two complementary diagnostics allowed to characterize the main structures in the interaction zone. By changing the gas composition and its density, the plasma cooling time can be controlled and one can pass from a quasiadiabatic outflow to a strongly radiation cooling jet. This tuning yields hydrodynamic structures very similar to those seen in astrophysical objects; the bow shock propagating through the gas, the shocked materials, the contact discontinuity, and the Machmore » disk. From a dimensional analysis, a scaling is made between both systems and shows the study relevance for the jet velocity, the Mach number, the jet-gas density ratio, and the dissipative processes. The use of a two-dimensional radiation hydrodynamic code, confirms the previous analysis and provides detailed structure of the interaction zone and energy repartition between jet and surrounding gases.« less

Ionization Waves of Arbitrary Velocity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turnbull, D.; Franke, P.; Katz, J.

The flying focus is a technique in which a chirped laser beam is focused by a chromatic lens to produce an extended focal spot within which laser intensity can propagate at any velocity. If the intensity is above the ionization threshold of a background gas, an ionization wave will track the ionization threshold intensity isosurface as it propagates. We report on the demonstration of such ionization waves of arbitrary velocity. Subluminal and superluminal ionization fronts were produced, both forward- and backward-propagating relative to the ionizing laser. In conclusion, all backward and all superluminal cases mitigated the issue of ionization-induced refractionmore » that typically challenges the formation of long, contiguous plasma channels.« less

Wave propagation in fiber composite laminates, part 2

NASA Technical Reports Server (NTRS)

Daniel, I. M.; Liber, T.

1976-01-01

An experimental investigation was conducted to determine the wave propagation characteristics, transient strains and residual properties in unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicone rubber projectiles at velocities up to 250 MS-1. The predominant wave is flexural, propagating at different velocities in different directions. In general, measured wave velocities were higher than theoretically predicted values. The amplitude of the in-plane wave is less than ten percent of that of the flexural wave. Peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers. The dynamics of impact were also studied with high speed photography.

Ionization Waves of Arbitrary Velocity

DOE PAGES

Turnbull, D.; Franke, P.; Katz, J.; ...

2018-05-31

The flying focus is a technique in which a chirped laser beam is focused by a chromatic lens to produce an extended focal spot within which laser intensity can propagate at any velocity. If the intensity is above the ionization threshold of a background gas, an ionization wave will track the ionization threshold intensity isosurface as it propagates. We report on the demonstration of such ionization waves of arbitrary velocity. Subluminal and superluminal ionization fronts were produced, both forward- and backward-propagating relative to the ionizing laser. In conclusion, all backward and all superluminal cases mitigated the issue of ionization-induced refractionmore » that typically challenges the formation of long, contiguous plasma channels.« less

a Numerical Study of Basic Coastal Upwelling Processes.

NASA Astrophysics Data System (ADS)

Li, Zhihong

Available from UMI in association with The British Library. Two-dimensional (2-D) and three-dimensional (3 -D) numerical models with a second order turbulence closure are developed for the study of coastal upwelling processes. A logarithmic coordinate system is introduced to obtain increased resolution in the regions near the surface and bottom where high velocity shear occurs and in the upwelling zone where its width is confined to the coast. In the experiments performed in the 2-D model an ocean initially at rest is driven by a spatially uniform alongshore wind-stress. There is a development of an offshore flow in the surface layer and an onshore flow below the surface layer. In the wind-stress direction there is a development of a coastal surface jet. The neglect of the alongshore pressure gradient leads to the intensification of the jet, and the concentration of the onshore flow in an over-developed Ekman layer yielding an unrealistic deepening of a bottom mixed layer. When bathymetric variations are introduced, some modifications in the dynamics of upwelling are observed. On the shelf region there is another upwelling zone and isotherms are interested with the bottom topography. When an alongshore pressure gradient is added externally into the model, the strength of the coastal jet decreases and a coastal undercurrent exists at greater depth. In addition the return onshore flow is largely independent of depth and the deepening of the bottom mixed layer disappears. In the experiments performed in the 3-D model a wind-stress with limited domain is used. Coastally trapped waves are generated and propagate along the coastline leading to a development of an alongshore pressure gradient, which has a significant effect on upwelling. The evolution of the alongshore flow, vertical velocity and the temperature is determined by both remote and local wind due to the propagation of waves. As the integration proceeds, the flow pattern becomes remarkably 3-dimensional. Finally the influence of bathymetric variations on upwelling processes is examined.

Estimating propagation velocity through a surface acoustic wave sensor

DOEpatents

Xu, Wenyuan; Huizinga, John S.

2010-03-16

Techniques are described for estimating the propagation velocity through a surface acoustic wave sensor. In particular, techniques which measure and exploit a proper segment of phase frequency response of the surface acoustic wave sensor are described for use as a basis of bacterial detection by the sensor. As described, use of velocity estimation based on a proper segment of phase frequency response has advantages over conventional techniques that use phase shift as the basis for detection.

Quasi-dynamic versus fully dynamic simulations of earthquakes and aseismic slip with and without enhanced coseismic weakening

NASA Astrophysics Data System (ADS)

Thomas, Marion Y.; Lapusta, Nadia; Noda, Hiroyuki; Avouac, Jean-Philippe

2014-03-01

Physics-based numerical simulations of earthquakes and slow slip, coupled with field observations and laboratory experiments, can, in principle, be used to determine fault properties and potential fault behaviors. Because of the computational cost of simulating inertial wave-mediated effects, their representation is often simplified. The quasi-dynamic (QD) approach approximately accounts for inertial effects through a radiation damping term. We compare QD and fully dynamic (FD) simulations by exploring the long-term behavior of rate-and-state fault models with and without additional weakening during seismic slip. The models incorporate a velocity-strengthening (VS) patch in a velocity-weakening (VW) zone, to consider rupture interaction with a slip-inhibiting heterogeneity. Without additional weakening, the QD and FD approaches generate qualitatively similar slip patterns with quantitative differences, such as slower slip velocities and rupture speeds during earthquakes and more propensity for rupture arrest at the VS patch in the QD cases. Simulations with additional coseismic weakening produce qualitatively different patterns of earthquakes, with near-periodic pulse-like events in the FD simulations and much larger crack-like events accompanied by smaller events in the QD simulations. This is because the FD simulations with additional weakening allow earthquake rupture to propagate at a much lower level of prestress than the QD simulations. The resulting much larger ruptures in the QD simulations are more likely to propagate through the VS patch, unlike for the cases with no additional weakening. Overall, the QD approach should be used with caution, as the QD simulation results could drastically differ from the true response of the physical model considered.

Observational discrimination between modes of shock propagation in interstellar clouds: Predictions of CH+ and SH+ column densities in diffuse clouds

NASA Technical Reports Server (NTRS)

Flower, D. R.; Desforets, G. P.; Roueff, E.; Hartquist, T. W.

1986-01-01

Considerable effort in recent years has been devoted to the study of shocks in the diffuse interstellar medium. This work has been motivated partly by the observations of rotationally excited states of H2, and partly by the realization that species such as CH(+), OH and H2O might be formed preferentially in hot, post-shock gas. The problem of CH(+) and the difficulties encountered when trying to explain the high column densities, observed along lines of sight to certain hot stars, have been reviewed earlier. The importance of a transverse magnetic field on the structure of an interstellar shock was also demonstrated earlier. Transverse magnetic fields above a critical strength give rise to an acceleration zone or precursor, in which the parameters on the flow vary continuously. Chemical reactions, which change the degree of ionization of the gas, also modify the structure of the shock considerably. Recent work has shown that large column densities of CH(+) can be produced in magnetohydrodynamic shock models. Shock speeds U sub s approx. = 10 km/s and initial magnetic field strengths of a few micro G are sufficient to produce ion-neutral drift velocities which can drive the endothermic C(+)(H2,H)CH(+) reaction. It was also shown that single-fluid hydrodynamic models do not generate sufficiently large column densities of CH(+) unless unacceptably high shock velocities (u sub s approx. 20 km/s) are assumed in the models. Thus, the observed column densities of CH(+) provide a constraint on the mode of shock propagation in diffuse clouds. More precisely, they determine a lower limit to the ion-neutral drift velocity.

Modelling sound propagation in the Southern Ocean to estimate the acoustic impact of seismic research surveys on marine mammals

NASA Astrophysics Data System (ADS)

Breitzke, Monika; Bohlen, Thomas

2010-05-01

Modelling sound propagation in the ocean is an essential tool to assess the potential risk of air-gun shots on marine mammals. Based on a 2.5-D finite-difference code a full waveform modelling approach is presented, which determines both sound exposure levels of single shots and cumulative sound exposure levels of multiple shots fired along a seismic line. Band-limited point source approximations of compact air-gun clusters deployed by R/V Polarstern in polar regions are used as sound sources. Marine mammals are simulated as static receivers. Applications to deep and shallow water models including constant and depth-dependent sound velocity profiles of the Southern Ocean show dipole-like directivities in case of single shots and tubular cumulative sound exposure level fields beneath the seismic line in case of multiple shots. Compared to a semi-infinite model an incorporation of seafloor reflections enhances the seismically induced noise levels close to the sea surface. Refraction due to sound velocity gradients and sound channelling in near-surface ducts are evident, but affect only low to moderate levels. Hence, exposure zone radii derived for different hearing thresholds are almost independent of the sound velocity structure. With decreasing thresholds radii increase according to a spherical 20 log10 r law in case of single shots and according to a cylindrical 10 log10 r law in case of multiple shots. A doubling of the shot interval diminishes the cumulative sound exposure levels by -3 dB and halves the radii. The ocean bottom properties only slightly affect the radii in shallow waters, if the normal incidence reflection coefficient exceeds 0.2.

What are the control mechanisms of evenly-spaced parallel strike-slip faults? Insights from DEM modeling

NASA Astrophysics Data System (ADS)

Bonilla Sierra, V.; Donze, F. V.; Duriez, J.; Klinger, Y.; Scholtes, L.

2016-12-01

At the very early stages of a pure strike-slip fault zone formation, shear displacement along a deep buried parent fault produces a characteristic set of "evenly-spaced" strike-slip faults at the surface, e.g. Southern San Andreas, North Anatolian, Central Asian, and Northern Tibetan fault systems. This mode III fracture propagation is initiated by the rotation of the local principal stress at the tip of the parent discontinuity, generating twisted fractures with a helicoidal shape. In sandbox or clay-cake experiments used to reproduce these structures, it has been observed that the spacing and possibly the characteristic length of the fractures appearing at the surface are proportional to the overburden thickness of the deformed layer. Based on a Discrete Element Method (YADE DEM-Open Source), we have investigated the conditions controlling the linear relationships between the spacing of the surface "evenly-spaced" strike-slip discontinuities and the thickness of the deformed layer. Increasing the basement displacement of the model, a diffused shear zone appears first at the tip of the basal parent discontinuity. From this mist zone, localized and strongly interacting shear fractures start to propagate. This interaction process can generate complex internal structures: some fractures will propagate faster than their neighbors, modifying their close surrounding stress environment. Some propagating fractures can stop growing and asymmetrical fracture sets can be observed. This resulting hierarchical bifurcation process leads to a set of "en echelon" discontinuities appearing at the surface (Figure 1). In a pure strike-slip mode, fracture spacing is proportional to the thickness, with a ratio and a bifurcation mode controlled by the cohesion value at the first order. Depending on the Poisson's ratio value, which mainly controls the orientation of the discontinuities, this ratio can be affected at a lower degree. In presence of mixed-mode (transpression or transtension), these linear relationships disappear. Figure 1: Effects of the cohesion C and the thickness T of the deformed layer on the surface discontinuity pattern (a) T = Tref and C = Cref (b) T = Tref and C= 10×Cref (c) T = 2×Tref and C = Cref (d) T = 2×Tref and 10×Cref. The color code corresponds to the instantaneous velocity in the Y direction.

Novel Devices Using Multifunctional ZnO and Its Nanostructures

DTIC Science & Technology

2008-12-01

bias, the electron density increases to a very high level, and the SAW will propagate with the slower short- circuit velocity, vsc . For intermediate...will propagate at a velocity v, which is between voc and vsc . The value of v will be determined by the charge density, the effective coupling of the

Scattering of S waves diffracted at the core-mantle boundary: forward modelling

NASA Astrophysics Data System (ADS)

Emery, Valérie; Maupin, Valérie; Nataf, Henri-Claude

1999-11-01

The lowermost 200-300 km of the Earth's mantle, known as the D'' layer, is an extremely complex and heterogeneous region where transfer processes between the core and the mantle take place. Diffracted S waves propagate over large distances and are very sensitive to the velocity structure of this region. Strong variations of ampli-tudes and waveforms are observed on recordings from networks of broad-band seismic stations. We perform forward modelling of diffracted S waves in laterally heterogeneous structures in order to analyse whether or not these observations can be related to lateral inhomogeneities in D''. We combine the diffraction due to the core and the scattering due to small-scale volumetric heterogeneities (10-100 km) by coupling single scattering (Born approximation) with the Langer approximation, which describes Sdiff wave propagation. The influence on the direct as well as on the scattered wavefields of the CMB as well as of possible tunnelling in the core or in D'' is fully accounted for. The SH and the SV components of the diffracted waves are analysed, as well as their coupling. The modelling is applied in heterogeneous models with different geometries: isolated heterogeneities, vertical cylinders, horizontal inhomogeneities and random media. Amplitudes of scattered waves are weak and only velocity perturbations of the order of 10 per cent over a volume of 240 x 240 x 300 km3 produce visible effects on seismograms. The two polarizations of Sdiff have different radial sensitivities, the SH components being more sensitive to heterogeneities closer to the CMB. However, we do not observe significant time-shifts between the two components similar to those produced by anisotropy. The long-period Sdiff have a poor lateral resolution and average the velocity perturbations in their Fresnel zone. Random small-scale heterogeneities with +/- 10 per cent velocity contrast in the layer therefore have little effect on Sdiff, in contrast to their effect on PKIKP.

Low Velocity Detonation of Nitromethane Affected by Precursor Shock Waves Propagating in Various Container Materials

NASA Astrophysics Data System (ADS)

Hamashima, H.; Osada, A.; Itoh, S.; Kato, Y.

2007-12-01

It is well known that some liquid explosives have two detonation behaviors, high velocity detonation (HVD) or low velocity detonation (LVD) can propagate. A physical model to describe the propagation mechanism of LVD in liquid explosives was proposed that LVD is not a self-reactive detonation, but rather a supported-reactive detonation from the cavitation field generated by precursor shock waves. However, the detailed structure of LVD in liquid explosives has not yet been clarified. In this study, high-speed photography was used to investigate the effects of the precursor shock waves propagating in various container materials for LVD in nitromethane (NM). Stable LVD was not observed in all containers, although transient LVD was observed. A very complicated structure of LVD was observed: the interaction of multiple precursor shock waves, multiple oblique shock waves, and the cavitation field.

Low Velocity Detonation of Nitromethane Affected by Precursor Shock Waves Propagating in Various Container Materials

NASA Astrophysics Data System (ADS)

Hamashima, Hideki; Osada, Akinori; Kato, Yukio; Itoh, Shigeru

2007-06-01

It is well known that some liquid explosives have two detonation behaviors, high velocity detonation (HVD) or low velocity detonation (LVD) can propagate. A physical model to describe the propagation mechanism of LVD in liquid explosives was proposed that LVD is not a self-reactive detonation, but rather a supported-reactive detonation from the cavitation field generated by precursor shock waves. However, the detailed structure of LVD in liquid explosives has not yet been clarified. In this study, high-speed photography was used to investigate the effects of the precursor shock waves propagating in various container materials for LVD in nitromethane (NM). Stable LVD was not observed in all containers, although transient LVD was observed. A very complicated structure of LVD was observed: the interaction of multiple precursor shock waves, multiple oblique shock waves, and the cavitation field.

Simulation study of axial ultrasound transmission in heterogeneous cortical bone model

NASA Astrophysics Data System (ADS)

Takano, Koki; Nagatani, Yoshiki; Matsukawa, Mami

2017-07-01

Ultrasound propagation in a heterogeneous cortical bone was studied. Using a bovine radius, the longitudinal wave velocity distribution in the axial direction was experimentally measured in the MHz range. The bilinear interpolation and piecewise cubic Hermite interpolation methods were applied to create a three-dimensional (3D) precise velocity model of the bone using experimental data. By assuming the uniaxial anisotropy of the bone, the distributions of all elastic moduli of a 3D heterogeneous model were estimated. The elastic finite-difference time-domain method was used to simulate axial ultrasonic wave propagation. The wave propagation in the initial model was compared with that in the thinner model, where the inner part of the cortical bone model was removed. The wave front of the first arriving signal (FAS) slightly depended on the heterogeneity in each model. Owing to the decrease in bone thickness, the propagation behavior also changed and the FAS velocity clearly decreased.

Three-dimensional mapping of extrusive layer at the East Pacific Rise 9°50'N

NASA Astrophysics Data System (ADS)

Marjanovic, M.; Stopin, A.; Plessix, R. E.; Singh, S. C.

2017-12-01

The East Pacific Rise (EPR) is one of the most active portion of Mid-Ocean Ridge system along which 6 km thick oceanic crust has been forming. The upper part of thus formed crust is represented by basalts (layer 2A) and dikes (layer 2B). In velocity models, the layer 2A/2B boundary is characterized by a velocity gradient, which is attributed to change in porosity. The geologic nature of the gradient is debated, with the two prevailing explanations: lithological contact between basalts and dikes, or alteration front due to hydrothermal circulation. In addition, 2D seismic sections suggested rapid thickening of the topmost layer within a few km from the ridge axis. Due to limited information on the upper crustal velocities it has been unclear if this observation is due to physical thickening of the extrusive layer or it is a result of downward propagating, hydrothermally driven, cracking front. To add some of the missing constrains, we apply elastic 3D full waveform inversion technique to 3D seismic dataset collected at the EPR. The final 3D velocity model of the upper crust covers area 44x55 km2, and is obtained after 15, multiparameter inversions of low frequencies. The layer 2A/2B boundary is clearly identified in the resulting model as the base of high velocity gradient and can be followed throughout the entire area included in the inversion; consistency in character of the gradient zone and distinct velocity anomaly near active hydrothermal discharge zones, where the most of the alteration is expected to take place, argue that this boundary is predominantly lithological and that the layer 2A thickening is due to emplacement of lava off the innermost axial zone. The transition from thin (150-200 m) to thick (300-550 m) layer 2A occurs within a narrow band around the ridge axis (0.5-2.5 km). This band is wider between 9º48-53', and highly asymmetric, with almost vertical side on the Pacific and gentle dipping side on the Cocos Plate, terminating at the contact with ridge parallel, inward facing faults. Beyond the faults, layer 2A attains almost constant thickness. By combining the available observables and results of our analyses we suggest that the emplacement of extrusives, variation in their thickness, and rate of dike subsidence are predominantly controlled by tectono-magmatic features and processes operating near the ridge axis.

Shallow seismic structure of Kunlun fault zone in northern Tibetan Plateau, China: Implications for the 2001 M s8.1 Kunlun earthquake

USGS Publications Warehouse

Wang, Chun-Yong; Mooney, W.D.; Ding, Z.; Yang, J.; Yao, Z.; Lou, H.

2009-01-01

The shallow seismic velocity structure of the Kunlun fault zone (KLFZ) was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions. The data were collected after the 2001 Kunlun M s8.1 earthquake in the northern Tibetan Plateau. Seismic phases for the in-line record sections (26 records up to a distance of 15 km) along the fault zone were analysed, and 1-D P- and S-wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method. Sixteen seismic stations were deployed along the off-line profile perpendicular to the fault zone. Fault-zone trapped waves appear clearly on the record sections, which were simulated with a 3-D finite difference algorithm. Quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the Kunlun fault-zone width is 300 m, and S-wave quality factor Q within the fault zone is 15. Significantly, S-wave velocities within the fault zone are reduced by 30-45 per cent from surrounding rocks to a depth of at least 1-2 km, while P-wave velocities are reduced by 7-20 per cent. A fault-zone with such P- and S-low velocities is an indication of high fluid pressure because Vs is affected more than Vp. The low-velocity and low-Q zone in the KLFZ model is the effect of multiple ruptures along the fault trace of the 2001 M s8.1 Kunlun earthquake. ?? 2009 The Authors Journal compilation ?? 2009 RAS.

Modelling of the combustion velocity in UIT-85 on sustainable alternative gas fuel

NASA Astrophysics Data System (ADS)

Smolenskaya, N. M.; Korneev, N. V.

2017-05-01

The flame propagation velocity is one of the determining parameters characterizing the intensity of combustion process in the cylinder of an engine with spark ignition. Strengthening of requirements for toxicity and efficiency of the ICE contributes to gradual transition to sustainable alternative fuels, which include the mixture of natural gas with hydrogen. Currently, studies of conditions and regularities of combustion of this fuel to improve efficiency of its application are carried out in many countries. Therefore, the work is devoted to modeling the average propagation velocities of natural gas flame front laced with hydrogen to 15% by weight of the fuel, and determining the possibility of assessing the heat release characteristics on the average velocities of the flame front propagation in the primary and secondary phases of combustion. Experimental studies, conducted the on single cylinder universal installation UIT-85, showed the presence of relationship of the heat release characteristics with the parameters of the flame front propagation. Based on the analysis of experimental data, the empirical dependences for determination of average velocities of flame front propagation in the first and main phases of combustion, taking into account the change in various parameters of engine operation with spark ignition, were obtained. The obtained results allow to determine the characteristics of heat dissipation and to assess the impact of addition of hydrogen to the natural gas combustion process, that is needed to identify ways of improvement of the combustion process efficiency, including when you change the throttling parameters.

Internal and External Match Loads of University-Level Soccer Players: A Comparison Between Methods.

PubMed

Sparks, Martinique; Coetzee, Ben; Gabbett, Tim J

2017-04-01

Sparks, M, Coetzee, B, and Gabbett, TJ. Internal and external match loads of university-level soccer players: a comparison between methods. J Strength Cond Res 31(4): 1072-7077, 2017-The aim of this study was to use individualized intensity zones to compare the external (velocity and player load, PL) and internal loads (heart rate, HR) of a cohort of university-level soccer players. Thirteen soccer players completed a 40-m maximum speed test and the Yo-Yo intermittent recovery test 1 (Yo-Yo IR1) to determine individualized velocity and HR thresholds. Heart rate values and global positioning system (GPS) data of each player were recorded during 5 league matches. A large (r = 0.46; p ≤ 0.01) correlation was found between time spent in the low-intensity (LI) velocity zone (LIVZ) and the LI HR zone. Similarly, there were moderate (r = 0.25; p ≤ 0.01) to large (r = 0.57; p ≤ 0.01) correlations between the relative and absolute time spent in the moderate-intensity (MI) velocity zone (MIVZ) and the MI HR zone. No significant correlations (p ≤ 0.01) existed between the high-intensity (HI) velocity zones (HIVZ) and the HI HR zone. On the other hand, PL showed significant correlations with all velocity and HR (absolute and relative) variables, with the exception of a nonsignificant correlation between the HI HR variables and PL. To conclude, PL showed good correlations with both velocity and HR zones and therefore may have the potential to serve as a good indicator of both external and internal soccer match loads.

The serpentine optical waveguide: engineering the dispersion relations and the stopped light points.

PubMed

Scheuer, Jacob; Weiss, Ori

2011-06-06

We present a study a new type of optical slow-light structure comprising a serpentine shaped waveguide were the loops are coupled. The dispersion relation, group velocity and GVD are studied analytically using a transfer matrix method and numerically using finite difference time domain simulations. The structure exhibits zero group velocity points at the ends of the Brillouin zone, but also within the zone. The position of mid-zone zero group velocity point can be tuned by modifying the coupling coefficient between adjacent loops. Closed-form analytic expressions for the dispersion relations, group velocity and the mid-zone zero v(g) points are found and presented.

A photoelectric technique for measuring lightning-channel propagation velocities from a mobile laboratory

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Rust, W. David

1989-01-01

The present device for lightning channel propagation-velocity determination employs eight photodetectors mounted behind precision horizontal slits in the focal plane of a photographic camera lens. The eight photodetector pulses, IRIG-B time, and slow and fast electric field-change waveforms are recorded on a 14-track analog tape recorder. A comparison of the present results with those obtained by a streaking camera shows no significant differences between the velocities obtained from the same strokes with the two systems; neither is there any difference in pulse characteristics or in the velocities calculated from them.

MX Siting Investigation. Geotechnical Evaluation of Luke Bombing and Gunnery Range. Geotechnical Report, Lechuguilla Desert, Arizona. Volume I.

DTIC Science & Technology

1978-01-20

8217-5000 -150 C KILOETERS , 1 2 V i asagerat- EXPLANATION i SURFICIAL BASIN FILL; Alluvial tans and playa lacustrine deposits; average seismic velocity...Undetermined e Velocity zone I represents alluvial fan deposits and possible playa /lacustrine materials underlying the unconsolidated, thin 1younger...alluvial fan unit (A5y, A5yf). Velocity zone 2 seems to represert older, playa /lacustrine deposits overlying Veloc- ity zone 3, which may be the well

Coseismic Traveling Ionospheric Disturbances during the Mw 7.8 Gorkha, Nepal, Earthquake on 25 April 2015 From Ground and Spaceborne Observations

NASA Astrophysics Data System (ADS)

Tulasi Ram, S.; Sunil, P. S.; Ravi Kumar, M.; Su, S.-Y.; Tsai, L. C.; Liu, C. H.

2017-10-01

Coseismic traveling ionospheric disturbances (CTIDs) and their propagation characteristics during Mw 7.8 Gorkha earthquake in Nepal on 25 April 2015 have been investigated using a suite of ground-based GPS receivers and broadband seismometers along with the spaceborne radio occultation observations over the Indian subcontinent region. Depletion in vertical total electron content, a so called ionospheric hole, is observed near the epicenter 9-11 min after the onset of earthquake. A positive pulse preceding the depletion, similar to N-shaped perturbation, propagating with an apparent velocity of 2.4 km/s is observed on the south. Further, the CTIDs in the southward direction are found to split in to fast ( 2.4-1.7 km/s) and slow ( 680-520 m/s) propagating modes at epicentral distances greater than 800 km. However, the velocities of fast mode CTIDs are significantly smaller than the surface Rayleigh wave velocity ( 3.7 km/s), indicating that they are not the true imprint of Rayleigh wave, instead, can probably be attributed to the superimposed wave front formed by the mixture of acoustic waves excited by main shock and propagating Rayleigh wave. The southward CTIDs are found to propagate at F2 region altitudes of 300-440 km captured by Constellation Observing System for Meteorology, Ionosphere and Climate radio occultation observations. The CTIDs with periods of 4-6 min are observed in all directions with significantly larger amplitudes and faster propagation velocities in south and east directions. The observed azimuthal asymmetry in the amplitudes and velocities of CTIDs are discussed in terms of the alignment with geomagnetic field and nature of surface crustal deformation during the earthquake.

Digital core based transmitted ultrasonic wave simulation and velocity accuracy analysis

NASA Astrophysics Data System (ADS)

Zhu, Wei; Shan, Rui

2016-06-01

Transmitted ultrasonic wave simulation (TUWS) in a digital core is one of the important elements of digital rock physics and is used to study wave propagation in porous cores and calculate equivalent velocity. When simulating wave propagates in a 3D digital core, two additional layers are attached to its two surfaces vertical to the wave-direction and one planar wave source and two receiver-arrays are properly installed. After source excitation, the two receivers then record incident and transmitted waves of the digital rock. Wave propagating velocity, which is the velocity of the digital core, is computed by the picked peak-time difference between the two recorded waves. To evaluate the accuracy of TUWS, a digital core is fully saturated with gas, oil, and water to calculate the corresponding velocities. The velocities increase with decreasing wave frequencies in the simulation frequency band, and this is considered to be the result of scattering. When the pore fluids are varied from gas to oil and finally to water, the velocity-variation characteristics between the different frequencies are similar, thereby approximately following the variation law of velocities obtained from linear elastic statics simulation (LESS), although their absolute values are different. However, LESS has been widely used. The results of this paper show that the transmission ultrasonic simulation has high relative precision.

Numerical modeling of seismic anomalies at impact craters on a laboratory scale

NASA Astrophysics Data System (ADS)

Wuennemann, K.; Grosse, C. U.; Hiermaier, S.; Gueldemeister, N.; Moser, D.; Durr, N.

2011-12-01

Almost all terrestrial impact craters exhibit a typical geophysical signature. The usually observed circular negative gravity anomaly and reduced seismic velocities in the vicinity of crater structures are presumably related to an approximately hemispherical zone underneath craters where rocks have experienced intense brittle plastic deformation and fracturing during formation (see Fig.1). In the framework of the "MEMIN" (multidisciplinary experimental and modeling impact crater research network) project we carried out hypervelocity cratering experiments at the Fraunhofer Institute for High-Speed Dynamics on a decimeter scale to study the spatiotemporal evolution of the damage zone using ultrasound, acoustic emission techniques, and numerical modeling of crater formation. 2.5-10 mm iron projectiles were shot at 2-5.5 km/s on dry and water-saturated sandstone targets. The target material was characterized before, during and after the impact with high spatial resolution acoustic techniques to detect the extent of the damage zone, the state of rocks therein and to record the growth of cracks. The ultrasound measurements are applied analog to seismic surveys at natural craters but used on a different - i.e. much smaller - scale. We compare the measured data with dynamic models of crater formation, shock, plastic and elastic wave propagation, and tensile/shear failure of rocks in the impacted sandstone blocks. The presence of porosity and pore water significantly affects the propagation of waves. In particular the crushing of pores due to shock compression has to be taken into account. We present preliminary results showing good agreement between experiments and numerical model. In a next step we plan to use the numerical models to upscale the results from laboratory dimensions to the scale of natural impact craters.

Corrosion Effects on the Fatigue Crack Propagation of Giga-Grade Steel and its Heat Affected Zone in pH Buffer Solutions for Automotive Application

NASA Astrophysics Data System (ADS)

Lee, H. S.

2018-03-01

Corrosion fatigue crack propagation test was conducted of giga-grade steel and its heat affected zone in pH buffer solutions, and the results were compared with model predictions. Pure corrosion effect on fatigue crack propagation, particularly, in corrosive environment was evaluated by means of the modified Forman equation. As shown in results, the average corrosion rate determined from the ratio of pure corrosion induced crack length to entire crack length under a cycle load were 0.11 and 0.37 for base metal and heat affected zone, respectively, with load ratio of 0.5, frequency of 0.5 and pH 10.0 environment. These results demonstrate new interpretation methodology for corrosion fatigue crack propagation enabling the pure corrosion effects on the behavior to be determined.

40 CFR 147.2912 - Operating requirements for wells authorized by rule.

Code of Federal Regulations, 2011 CFR

2011-07-01

... does not initiate new fractures or propagate existing fractures in the confining zone adjacent to any... initiate new fractures or propagate existing fractures in the confining zone adjacent to any USDW; and (B) Submit data acceptable to the Regional Administrator which defines the fracture pressure of the formation...

40 CFR 147.2912 - Operating requirements for wells authorized by rule.

Code of Federal Regulations, 2014 CFR

2014-07-01

... does not initiate new fractures or propagate existing fractures in the confining zone adjacent to any... initiate new fractures or propagate existing fractures in the confining zone adjacent to any USDW; and (B) Submit data acceptable to the Regional Administrator which defines the fracture pressure of the formation...

40 CFR 147.2912 - Operating requirements for wells authorized by rule.

Code of Federal Regulations, 2012 CFR

2012-07-01

... does not initiate new fractures or propagate existing fractures in the confining zone adjacent to any... initiate new fractures or propagate existing fractures in the confining zone adjacent to any USDW; and (B) Submit data acceptable to the Regional Administrator which defines the fracture pressure of the formation...

40 CFR 147.2912 - Operating requirements for wells authorized by rule.

Code of Federal Regulations, 2013 CFR

2013-07-01

... does not initiate new fractures or propagate existing fractures in the confining zone adjacent to any... initiate new fractures or propagate existing fractures in the confining zone adjacent to any USDW; and (B) Submit data acceptable to the Regional Administrator which defines the fracture pressure of the formation...

Do scaly clays control seismicity on faulted shale rocks?

NASA Astrophysics Data System (ADS)

Orellana, Luis Felipe; Scuderi, Marco M.; Collettini, Cristiano; Violay, Marie

2018-04-01

One of the major challenges regarding the disposal of radioactive waste in geological formations is to ensure isolation of radioactive contamination from the environment and the population. Shales are suitable candidates as geological barriers. However, the presence of tectonic faults within clay formations put the long-term safety of geological repositories into question. In this study, we carry out frictional experiments on intact samples of Opalinus Clay, i.e. the host rock for nuclear waste storage in Switzerland. We report experimental evidence suggesting that scaly clays form at low normal stress (≤20 MPa), at sub-seismic velocities (≤300 μm/s) and is related to pre-existing bedding planes with an ongoing process where frictional sliding is the controlling deformation mechanism. We have found that scaly clays show a velocity-weakening and -strengthening behaviour, low frictional strength, and poor re-strengthening over time, conditions required to allow the potential nucleation and propagation of earthquakes within the scaly clays portion of the formation. The strong similarities between the microstructures of natural and experimental scaly clays suggest important implications for the slip behaviour of shallow faults in shales. If natural and anthropogenic perturbations modify the stress conditions of the fault zone, earthquakes might have the potential to nucleate within zones of scaly clays controlling the seismicity of the clay-rich tectonic system, thus, potentially compromising the long-term safeness of geological repositories situated in shales.

Long-Wavelength Elastic Wave Propagation Across Naturally Fractured Rock Masses

NASA Astrophysics Data System (ADS)

Mohd-Nordin, Mohd Mustaqim; Song, Ki-Il; Cho, Gye-Chun; Mohamed, Zainab

2014-03-01

Geophysical site investigation techniques based on elastic waves have been widely used to characterize rock masses. However, characterizing jointed rock masses by using such techniques remains challenging because of a lack of knowledge about elastic wave propagation in multi-jointed rock masses. In this paper, the roughness of naturally fractured rock joint surfaces is estimated by using a three-dimensional (3D) image-processing technique. The classification of the joint roughness coefficient (JRC) is enhanced by introducing the scan line technique. The peak-to-valley height is selected as a key indicator for JRC classification. Long-wavelength P-wave and torsional S-wave propagation across rock masses containing naturally fractured joints are simulated through the quasi-static resonant column (QSRC) test. In general, as the JRC increases, the S-wave velocity increases within the range of stress levels considered in this paper, whereas the P-wave velocity and the damping ratio of the shear wave decrease. In particular, the two-dimensional joint specimen underestimates the S-wave velocity while overestimating the P-wave velocity. This suggests that 3D joint surfaces should be implicated to obtain the reliable elastic wave velocity in jointed rock masses. The contact characteristic and degree of roughness and waviness of the joint surface are identified as a factor influencing P-wave and S-wave propagation in multi-jointed rock masses. The results indicate a need for a better understanding of the sensitivity of contact area alterations to the elastic wave velocity induced by changes in normal stress. This paper's framework can be a reference for future research on elastic wave propagation in naturally multi-jointed rock masses.

The release of trapped gases from amorphous solid water films. I. "Top-down" crystallization-induced crack propagation probed using the molecular volcano.

PubMed

May, R Alan; Smith, R Scott; Kay, Bruce D

2013-03-14

In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104502 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization of ASW, a phenomenon that we termed the "molecular volcano." The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper, we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length distribution is independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2, or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ∕mol. This value is consistent with the crystallization growth rates reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization∕crack front into the film is in good agreement with the temperature programmed desorption results.

The Release of Trapped Gases from Amorphous Solid Water Films: I. “Top-Down” Crystallization-Induced Crack Propagation Probed using the Molecular Volcano

DOE Office of Scientific and Technical Information (OSTI.GOV)

May, Robert A.; Smith, R. Scott; Kay, Bruce D.

In this (Paper I) and the companion paper (Paper II) we investigate the mechanisms for the release of trapped gases from underneath of amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization ASW, a phenomenon that we termed the "molecular volcano". The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length and distributionmore » are independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2 or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ/mol. This value is consistent with the crystallization growth rate reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization/crack front into the film is in good agreement with the temperature programmed desorption results.« less

Anisotropic changes in P-wave velocity and attenuation during deformation and fluid infiltration of granite

USGS Publications Warehouse

Stanchits, S.A.; Lockner, D.A.; Ponomarev, A.V.

2003-01-01

Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic-wave propagation characteristics such as Vp/Vs ratio, attenuation, and reflectivity contacts. We present laboratory measurements of changes in P-wave velocity and attenuation during the injection of water into a granite sample as it was loaded to failure. A cylindrical sample of Westerly granite was deformed at constant confining and pore pressures of 50 and 1 MPa, respectively. Axial load was increased in discrete steps by controlling axial displacement. Anisotropic P-wave velocity and attenuation fields were determined during the experiment using an array of 13 piezoelectric transducers. At the final loading steps (86% and 95% of peak stress), both spatial and temporal changes in P-wave velocity and peak-to-peak amplitudes of P and S waves were observed. P-wave velocity anisotropy reached a maximum of 26%. Transient increases in attenuation of up to 483 dB/m were also observed and were associated with diffusion of water into the sample. We show that velocity and attenuation of P waves are sensitive to the process of opening of microcracks and the subsequent resaturation of these cracks as water diffuses in from the surrounding region. Symmetry of the orientation of newly formed microcracks results in anisotropic velocity and attenuation fields that systematically evolve in response to changes in stress and influx of water. With proper scaling, these measurements provide constraints on the magnitude and duration of velocity and attenuation transients that can be expected to accompany the nucleation of earthquakes in the Earth's crust.

Infragravity wave generation and dynamics over a mild slope beach : Experiments and numerical computations

NASA Astrophysics Data System (ADS)

Cienfuegos, R.; Duarte, L.; Hernandez, E.

2008-12-01

Charasteristic frequencies of gravity waves generated by wind and propagating towards the coast are usually comprised between 0.05Hz and 1Hz. Nevertheless, lower frequecy waves, in the range of 0.001Hz and 0.05Hz, have been observed in the nearshore zone. Those long waves, termed as infragravity waves, are generated by complex nonlinear mechanisms affecting the propagation of irregular waves up to the coast. The groupiness of an incident random wave field may be responsible for producing a slow modulation of the mean water surface thus generating bound long waves travelling at the group speed. Similarly, a quasi- periodic oscillation of the break-point location, will be accompained by a slow modulation of set-up/set-down in the surf zone and generation and release of long waves. If the primary structure of the carrying incident gravity waves is destroyed (e.g. by breaking), forced long waves can be freely released and even reflected at the coast. Infragravity waves can affect port operation through resonating conditions, or strongly affect sediment transport and beach morphodynamics. In the present study we investigate infragravity wave generation mechanisms both, from experiments and numerical computations. Measurements were conducted at the 70-meter long wave tank, located at the Instituto Nacional de Hidraulica (Chile), prepared with a beach of very mild slope of 1/80 in order to produce large surf zone extensions. A random JONSWAP type wave field (h0=0.52m, fp=0.25Hz, Hmo=0.17m) was generated by a piston wave-maker and measurements of the free surface displacements were performed all over its length at high spatial resolution (0.2m to 1m). Velocity profiles were also measured at four verticals inside the surf zone using an ADV. Correlation maps of wave group envelopes and infragravity waves are computed in order to identify long wave generation and dynamics in the experimental set-up. It appears that both mechanisms (groupiness and break-point oscillation) are clearly present in this experiment while spectral analysis evidences the reorganization of energy density from the original narrow spectrum into the infragravity band. This experiment provides an opportunity to test numerical models that would in principle be able to reproduce infragravity wave generation and dynamics. We compare numerical results (free surface and velocities) produced by a fully nonlinear Boussinesq model including breaking and runup to the experimental data and show that the complex infragravity wave dynamics is adequately reproduced by the model.

Toward the azimuthal characteristics of ionospheric and seismic effects of "Chelyabinsk" meteorite fall according to the data from coherent radar, GPS, and seismic networks

NASA Astrophysics Data System (ADS)

Berngardt, O. I.; Perevalova, N. P.; Dobrynina, A. A.; Kutelev, K. A.; Shestakov, N. V.; Bakhtiarov, V. F.; Kusonsky, O. A.; Zagretdinov, R. V.; Zherebtsov, G. A.

2015-12-01

We present the results of a study of the azimuthal characteristics of ionospheric and seismic effects of the meteorite `Chelyabinsk,' based on the data from the network of GPS receivers, coherent decameter radar EKB, and network of seismic stations, located near the meteorite fall trajectory. It is shown that 6-14 min after the bolide explosion, GPS network observed the cone-shaped wavefront of traveling ionospheric disturbances (TIDs) that is interpreted as a ballistic acoustic wave. The typical TIDs propagation velocity were observed 661 ± 256 m/s, which corresponds to the expected acoustic wave speed for 240 km height. Fourteen minutes after the bolide explosion, at distances of 200 km, we observed the emergence and propagation of a TID with annular wavefront that is interpreted as gravitational mode of internal atmospheric waves. The propagation velocity of this TID was 337 ± 89 m/s which corresponds to the propagation velocity of these waves in similar situations. At EKB radar, we observed TIDs in the sector of azimuthal angles close to the perpendicular to the meteorite trajectory. The observed TID velocity (400 m/s) and azimuthal properties correlate well with the model of ballistic wave propagating at 120-140 km altitude. It is shown that the azimuthal distribution of the amplitude of vertical seismic oscillations with periods 3-60 s can be described qualitatively by the model of vertical strike-slip rupture, propagating at 1 km/s along the meteorite fall trajectory to distance of about 40 km. These parameters correspond to the direction and velocity of propagation of the ballistic wave peak by the ground. It is shown that the model of ballistic wave caused by supersonic motion and burning of the meteorite in the upper atmosphere can satisfactorily explain the various azimuthal ionospheric effects, observed by the coherent decameter radar EKB, GPS receivers network, and the azimuthal characteristics of seismic waves at large distances.

Seismic Tomography Reveals Breaking Crust and Lithosphere Beneath a Classic Orogen

NASA Astrophysics Data System (ADS)

Byrne, T. B.; Rau, R.; Kuo-Chen, H.; Lee, Y.; Ouimet, W. B.; Van Soest, M. C.; Huang, C.; Wu, F. T.

2013-12-01

The orogenic system in Taiwan is often considered a classic example of an accretionary prism that has grown to a steady-state size and shape above an also steady subduction zone. A new study of vertical and horizontal sections of a tomographic velocity model created by Kuo-Chen et al. (2012) show, however, both a well-developed crack in the subducted crust beneath southern Taiwan and a discontinuous lithosphere beneath northern Taiwan, suggesting that slab breakoff is actively occurring beneath Taiwan. The transition from slab breakoff to cracking crust in southern Taiwan also suggests that slab breakoff is propagating southward, consistent an oblique collision. The crack in the subducting crust is revealed by progressively deeper horizontal sections of the local-scale tomographic model. The sections show an ellipsoidal-shaped area of high velocity that plunges southeast, oblique to all of the regional trends. Taking into account the dip of the slab, however, the area of high velocity is nearly parallel to previously recognized fracture zone in the Eurasian continental margin. We interpret the area of high velocity to be a crack in the Eurasian crust that is filled high velocity Eurasian mantle. Support for this interpretation comes from: 1) new exhumation cooling data from Mt Yu, the highest peak in Taiwan; 2) a recent leveling survey along the South Cross-Island Highway that shows unusually high rates of surface uplift (up to 15 mm/yr; Ching et al., 2011); 3) Vp attenuation studies that suggest anomalously high temperatures and/or the presence of fluids; 4) earthquake focal mechanisms in the core of the southern Central Range that are dominated by NE-SW extension; and finally, 5) the core of the southern Central Range preserves anomalous areas of low topographic relief that straddle the crest of the range. The areas of low relief are fringed by stream channels with relatively high stream gradient indexes and do not appear related to weaker rock types, glacial erosion, or lower rock uplift rates along the range crest. We propose that the surfaces represent relict topography that formed prior to a recent acceleration in rock uplift rate, consistent with the presence of a propagating crustal-scale crack and slab breakoff. Taken together, these results raise questions about the notion of steady state topography and critically tapered wedges in Taiwan. Kuo-Chen, H., Wu, F., and Roecker, S. W., 2012, Three-dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets: Journal Geophysical Research, v. 117, no. B06306. Ching, K.-E., Hsieh, M.-L., Johnson, K., Chen, K.-H., Rau, R.-J., and Yang, M., 2011, Modern vertical deformation rates and mountain building in Taiwan from precise leveling and continuous GPS observations, 2000-2008: Journal Geophysical Research, v. 116, no. B08406.

The effect of gradational velocities and anisotropy on fault-zone trapped waves

NASA Astrophysics Data System (ADS)

Gulley, A. K.; Eccles, J. D.; Kaipio, J. P.; Malin, P. E.

2017-08-01

Synthetic fault-zone trapped wave (FZTW) dispersion curves and amplitude responses for FL (Love) and FR (Rayleigh) type phases are analysed in transversely isotropic 1-D elastic models. We explore the effects of velocity gradients, anisotropy, source location and mechanism. These experiments suggest: (i) A smooth exponentially decaying velocity model produces a significantly different dispersion curve to that of a three-layer model, with the main difference being that Airy phases are not produced. (ii) The FZTW dispersion and amplitude information of a waveguide with transverse-isotropy depends mostly on the Shear wave velocities in the direction parallel with the fault, particularly if the fault zone to country-rock velocity contrast is small. In this low velocity contrast situation, fully isotropic approximations to a transversely isotropic velocity model can be made. (iii) Fault-aligned fractures and/or bedding in the fault zone that cause transverse-isotropy enhance the amplitude and wave-train length of the FR type FZTW. (iv) Moving the source and/or receiver away from the fault zone removes the higher frequencies first, similar to attenuation. (v) In most physically realistic cases, the radial component of the FR type FZTW is significantly smaller in amplitude than the transverse.

Traction–separation relationships for hydrogen induced grain boundary embrittlement in nickel via molecular dynamics simulations

DOE PAGES

Barrows, Wesley; Dingreville, Rémi; Spearot, Douglas

2015-10-19

A statistical approach combined with molecular dynamics simulations is used to study the influence of hydrogen on intergranular decohesion. This methodology is applied to a Ni Σ3(112)[11¯0] symmetric tilt grain boundary. Hydrogenated grain boundaries with different H concentrations are constructed using an energy minimization technique with initial H atom positions guided by Monte Carlo simulation results. Decohesion behavior is assessed through extraction of a traction–separation relationship during steady-state crack propagation in a statistically meaningful approach, building upon prior work employing atomistic cohesive zone volume elements (CZVEs). A sensitivity analysis is performed on the numerical approach used to extract the traction–separationmore » relationships, clarifying the role of CZVE size, threshold parameters necessary to differentiate elastic and decohesion responses, and the numerical averaging technique. Results show that increasing H coverage at the Ni Σ3(112)[11¯0] grain boundary asymmetrically influences the crack tip velocity during propagation, leads to a general decrease in the work of separation required for crack propagation, and provides a reduction in the peak stress in the extracted traction–separation relationship. Furthermore the present framework offers a meaningful vehicle to pass atomistically derived interfacial behavior to higher length scale formulations for intergranular fracture.« less

Geophysical evidence for a transform margin offshore Western Algeria: a witness of a subduction-transform edge propagator?

NASA Astrophysics Data System (ADS)

Badji, Rabia; Charvis, Philippe; Bracene, Rabah; Galve, Audrey; Badsi, Madjid; Ribodetti, Alessandra; Benaissa, Zahia; Klingelhoefer, Frauke; Medaouri, Mourad; Beslier, Marie-Odile

2015-02-01

For the first time, a deep seismic data set acquired in the frame of the Algerian-French SPIRAL program provides new insights regarding the origin of the westernmost Algerian margin and basin. We performed a tomographic inversion of traveltimes along a 100-km-long wide-angle seismic profile shot over 40 ocean bottom seismometers offshore Mostaganem (Northwestern Algeria). The resulting velocity model and multichannel seismic reflection profiles show a thin (3-4 km thick) oceanic crust. The narrow ocean-continent transition (less than 10 km wide) is bounded by vertical faults and surmounted by a narrow almost continuous basin filled with Miocene to Quaternary sediments. This fault system, as well as the faults organized in a negative-flower structure on the continent side, marks a major strike-slip fault system. The extremely sharp variation of the Moho depth (up to 45 ± 3°) beneath the continental border underscores the absence of continental extension in this area. All these features support the hypothesis that this part of the margin from Oran to Tenes, trending N65-N70°E, is a fossil subduction-transform edge propagator fault, vestige of the propagation of the edge of the Gibraltar subduction zone during the westward migration of the Alborán domain.

Propagation of the Semidiurnal Internal Tide: Phase Velocity Versus Group Velocity

NASA Astrophysics Data System (ADS)

Zhao, Zhongxiang

2017-12-01

The superposition of two waves of slightly different wavelengths has long been used to illustrate the distinction between phase velocity and group velocity. The first-mode M2 and S2 internal tides exemplify such a two-wave model in the natural ocean. The M2 and S2 tidal frequencies are 1.932 and 2 cycles per day, respectively, and their superposition forms a spring-neap cycle in the semidiurnal band. The spring-neap cycle acts like a wave, with its frequency, wave number, and phase being the differences of the M2 and S2 internal tides. The spring-neap cycle and energy of the semidiurnal internal tide propagate at the group velocity. Long-range propagation of M2 and S2 internal tides in the North Pacific is observed by satellite altimetry. Along a 3,400 km beam spanning 24°-54°N, the M2 and S2 travel times are 10.9 and 11.2 days, respectively. For comparison, it takes the spring-neap cycle 21.1 days to travel over this distance. Spatial maps of the M2 phase velocity, the S2 phase velocity, and the group velocity are determined from phase gradients of the corresponding satellite observed internal tide fields. The observed phase and group velocities agree with theoretical values estimated using the World Ocean Atlas 2013 annual-mean ocean stratification.

Imaging the crustal magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii

USGS Publications Warehouse

Okubo, Paul G.; Benz, Harley M.; Chouet, Bernard A.

1997-01-01

Three-dimensional seismic P-wave traveltime tomography is used to image the magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii. High-velocity bodies (>6.4 km/s) in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro-ultramafic cumulates from which the surface volcanism is derived. The proximity of these high-velocity features to the rift zones is consistent with a ridge-spreading model of the volcanic flank. Southeast of the Hilina fault zone, along the south flank of Kilauea, low-velocity material (<6.0 km/s) is observed extending to depths of 9–11 km, indicating that the Hilina fault may extend possibly as deep as the basal decollement. Along the southeast flank of Mauna Loa, a similar low-velocity zone associated with the Kaoiki fault zone is observed extending to depths of 6–8 km. These two upper crustal low-velocity zones suggest common stages in the evolution of the Hawaiian shield volcanoes in which these fault systems are formed as a result of upper crustal deformation in response to magma injection within the volcanic edifice.

Seismic evidence for water transport out of the mantle transition zone beneath the European Alps

NASA Astrophysics Data System (ADS)

Liu, Zhen; Park, Jeffrey; Karato, Shun-ichiro

2018-01-01

The mantle transition zone has been considered a major water reservoir in the deep Earth. Mass transfer across the transition-zone boundaries may transport water-rich minerals from the transition zone into the water-poor upper or lower mantle. Water release in the mantle surrounding the transition zone could cause dehydration melting and produce seismic low-velocity anomalies if some conditions are met. Therefore, seismic observations of low-velocity layers surrounding the transition zone could provide clues of water circulation at mid-mantle depths. Below the Alpine orogen, a depressed 660-km discontinuity has been imaged clearly using seismic tomography and receiver functions, suggesting downwellings of materials from the transition zone. Multitaper-correlation receiver functions show prominent ∼0.5-1.5% velocity reductions at ∼750-800-km depths, possibly caused by partial melting in the upper part of lower mantle. The gap between the depressed 660-km discontinuity and the low-velocity layers is consistent with metallic iron as a minor phase in the topmost lower mantle reported by laboratory studies. Velocity drops atop the 410-km discontinuity are observed surrounding the Alpine orogeny, suggesting upwelling of water-rich rock from the transition zone in response to the downwelled materials below the orogeny. Our results provide evidence that convective penetration of the mantle transition zone pushes hydrated minerals both upward and downward to add hydrogen to the surrounding mantle.

Radiation from a current filament driven by a traveling wave

NASA Technical Reports Server (NTRS)

Levine, D. M.; Meneghini, R.

1976-01-01

Solutions are presented for the electromagnetic fields radiated by an arbitrarily oriented current filament located above a perfectly conducting ground plane and excited by a traveling current wave. Both an approximate solution, valid in the fraunhofer region of the filament and predicting the radiation terms in the fields, and an exact solution, which predicts both near and far field components of the electromagnetic fields, are presented. Both solutions apply to current waveforms which propagate along the channel but are valid regardless of the actual waveshape. The exact solution is valid only for waves which propagate at the speed of light, and the approximate solution is formulated for arbitrary velocity of propagation. The spectrum-magnitude of the fourier transform-of the radiated fields is computed by assuming a compound exponential model for the current waveform. The effects of channel orientation and length, as well as velocity of propagation of the current waveform and location of the observer, are discussed. It is shown that both velocity of propagation and an effective channel length are important in determining the shape of the spectrum.

On the nature of regional seismic phases-III. The influence of crustal heterogeneity on the wavefield for subduction earthquakes: the 1985 Michoacan and 1995 Copala, Guerrero, Mexico earthquakes

NASA Astrophysics Data System (ADS)

Furumura, T.; Kennett, B. L. N.

1998-12-01

The most prominent feature of the regional seismic wavefield from about 150 to over 1000 km is usually the Lg phase. This arrival represents trapped S-wave propagation within the crust as a superposition of multiple reflections, and its amplitude is quite sensitive to the lateral variation in the crust along a propagation path. In an environment where the events occur in a subduction zone, such as the western coast of Mexico, quite complex influences on the character of the regional wavefield arise from the presence of the subduction zone. The great 1985 Michoacan earthquake (MW=8.1), which occurred in the Mexican subduction zone, was one of the most destructive earthquakes in modern history and its notable character was that at Mexico City, located over 350 km from the epicentre, there was strong ground shaking almost comparable to that in the epicentral region that lasted for several minutes. Considerable effort has been expended to explain the origin of the unusual observed waves that caused the severe damage in the capital city during the destructive earthquake. The nature of the propagation process in this region can be understood in part by using the detailed strong-motion records from the 1995 Copala, Guerrero (MW=7.4) earthquake near the coast to the south of Mexico City, which also had an enhanced amplitude in the Valley of Mexico. Numerical modelling of both P and S seismic waves in 2-D and 3-D heterogeneous crustal models for western Mexico using the pseudospectral method provides direct insight into the nature of the propagation processes through the use of sequences of snapshots of the wavefield and synthetic seismograms at the surface. A comparison of different models allows the influences of different aspects of the structure to be isolated. 2-D and 3-D modelling of the 1985 Michoacan and 1995 Copala earthquakes clearly demonstrates that the origin of the long duration of strong ground shaking comes from the Sn and Lg wave trains. These S-wave arrivals are produced efficiently from shallow subduction earthquakes and are strongly enhanced during their propagation within the laterally heterogeneous waveguide produced by the subduction of the Cocos Plate beneath the Mexican mainland. The amplitude and duration of the Lg coda is also strongly reinforced by transmission through the Mexican Volcanic Belt from the amplification of S waves in the low-velocity surficial layer associated withS-to-P conversions in the volcanic zone. The further amplification of the large and long Lg wave train impinging on the shallow structure in the basin of Mexico City, with very soft soil underlain by nearly rigid bedrock with a strong impedance contrast, gives rise to the destructive strong ground shaking from the Mexican subduction earthquakes.

Wrinkle-like slip pulse on a fault between different materials

USGS Publications Warehouse

Andrews, D.J.; Ben-Zion, Y.

1997-01-01

Pulses of slip velocity can propagate on a planar interface governed by a constant coefficient of friction, where the interface separates different elastic materials. Such pulses have been found in two-dimensional plane strain finite difference calculations of slip on a fault between elastic media with wave speeds differing by 20%. The self-sustaining propagation of the slip pulse arises from interaction between normal and tangential deformation that exists only with a material contrast. These calculations confirm the prediction of Weertman [1980] that a dislocation propagating steadily along a material interface has a tensile change of normal traction with the same pulse shape as slip velocity. The self-sustaining pulse is associated with a rapid transition from a head wave traveling along the interface with the S wave speed of the faster material, to an opposite polarity body wave traveling with the slower S speed. Slip occurs during the reversal of normal particle velocity. The pulse can propagate in a region with constant coefficient of friction and an initial stress state below the frictional criterion. Propagation occurs in only one direction, the direction of slip in the more compliant medium, with rupture velocity near the slower S wave speed. Displacement is larger in the softer medium, which is displaced away from the fault during the passage of the slip pulse. Motion is analogous to a propagating wrinkle in a carpet. The amplitude of slip remains approximately constant during propagation, but the pulse width decreases and the amplitudes of slip velocity and stress change increase. The tensile change of normal traction increases until absolute normal traction reaches zero. The pulse can be generated as a secondary effect of a drop of shear stress in an asperity. The pulse shape is unstable, and the initial slip pulse can change during propagation into a collection of sharper pulses. Such a pulse enables slip to occur with little loss of energy to friction, while at the same time increasing irregularity of stress and slip at the source. Copyright 1997 by the American Geophysical Union.

Volcano-tectonic implications of 3-D velocity structures derived from joint active and passive source tomography of the island of Hawaii

USGS Publications Warehouse

Park, J.; Morgan, J.K.; Zelt, C.A.; Okubo, P.G.

2009-01-01

We present a velocity model of the onshore and offshore regions around the southern part of the island of Hawaii, including southern Mauna Kea, southeastern Hualalai, and the active volcanoes of Mauna Loa, and Kilauea, and Loihi seamount. The velocity model was inverted from about 200,000 first-arrival traveltime picks of earthquakes and air gun shots recorded at the Hawaiian Volcano Observatory (HVO). Reconstructed volcanic structures of the island provide us with an improved understanding of the volcano-tectonic evolution of Hawaiian volcanoes and their interactions. The summits and upper rift zones of the active volcanoes are characterized by high-velocity materials, correlated with intrusive magma cumulates. These high-velocity materials often do not extend the full lengths of the rift zones, suggesting that rift zone intrusions may be spatially limited. Seismicity tends to be localized seaward of the most active intrusive bodies. Low-velocity materials beneath parts of the active rift zones of Kilauea and Mauna Loa suggest discontinuous rift zone intrusives, possibly due to the presence of a preexisting volcanic edifice, e.g., along Mauna Loa beneath Kilauea's southwest rift zone, or alternatively, removal of high-velocity materials by large-scale landsliding, e.g., along Mauna Loa's western flank. Both locations also show increased seismicity that may result from edifice interactions or reactivation of buried faults. New high-velocity regions are recognized and suggest the presence of buried, and in some cases, previously unknown rift zones, within the northwest flank of Mauna Loa, and the south flanks of Mauna Loa, Hualalai, and Mauna Kea. Copyright 2009 by the American Geophysical Union.

Strong Ground Motion Generation during the 2011 Tohoku-Oki Earthquake

NASA Astrophysics Data System (ADS)

Asano, K.; Iwata, T.

2011-12-01

Strong ground motions during the 2011 Tohoku-Oki earthquake (Mw9.0) were densely observed by the strong motion observation networks all over Japan. Seeing the acceleration and velocity waveforms observed at strong stations in northeast Japan along the source region, those ground motions are characterized by plural wave packets with duration of about twenty seconds. Particularly, two wave packets separated by about fifty seconds could be found on the records in the northern part of the damaged area, whereas only one significant wave packets could be recognized on the records in the southern part of the damaged area. The record section shows four isolated wave packets propagating from different locations to north and south, and it gives us a hint of the strong motion generation process on the source fault which is related to the heterogeneous rupture process in the scale of tens of kilometers. In order to solve it, we assume that each isolated wave packet is contributed by the corresponding strong motion generation area (SMGA). It is a source patch whose slip velocity is larger than off the area (Miyake et al., 2003). That is, the source model of the 2011 Tohoku-Oki earthquake consists of four SMGAs. The SMGA source model has succeeded in reproducing broadband strong ground motions for past subduction-zone events (e.g., Suzuki and Iwata, 2007). The target frequency range is set to be 0.1-10 Hz in this study as this range is significantly related to seismic damage generation to general man-made structures. First, we identified the rupture starting points of each SMGA by picking up the onset of individual packets. The source fault plane is set following the GCMT solution. The first two SMGAs were located approximately 70 km and 30 km west of the hypocenter. The third and forth SMGAs were located approximately 160 km and 230 km southwest of the hypocenter. Then, the model parameters (size, rise time, stress drop, rupture velocity, rupture propagation pattern) of these four SMGAs were determined by waveform modeling using the empirical Green's function method (Irikura, 1986). The first and second SMGAs are located close to each other, and they are partially overlapped though the difference in the rupture time between them is more than 40 s. Those two SMGA appear to be included in the source region of the past repeating Miyagi-Oki subduction-zone event in 1936. The third and fourth SMGAs appear to be located in the source region of the past Fukushima-Oki events in 1938. Each of Those regions has been expected to cause next major earthquakes in the long-term evaluation. The obtained source model explains the acceleration, velocity, and displacement time histories in the target frequency range at most stations well. All of four SMGAs exist apparently outside of the large slip area along the trench east of the hypocenter, which was estimated by the seismic, geodetic, and tsunami inversion analyses, and this large slip zone near the trench does not contribute to strong motion much. At this point, we can conclude that the 2011 Tohoku-Oki earthquake has a possibility to be a complex event rupturing multiple preexisting asperities in terms of strong ground motion generation. It should be helpful to validate and improve the applicability of the strong motion prediction recipe for great subduction-zone earthquakes.

Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Gangloff, Richard P.

1992-01-01

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

The influence of annealing on domain wall propagation in bistable amorphous microwire with unidirectional effect

NASA Astrophysics Data System (ADS)

Onufer, Jozef; Ziman, Ján; Duranka, Peter; Kladivová, Mária

2018-07-01

The effect of gradual annealing on the domain wall mobility (velocity), nucleation, critical depinning and propagation fields in amorphous FeSiB microwires has been studied. A new experimental set-up, presented in this paper, allows measurement of average domain wall velocity for four different conditions and detection of the presence of unidirectional effect in wall propagation without manipulation of the microwire. The proposed interpretation is that a domain wall is considered as a relatively long object which can change its axial dimension due to inhomogeneity of damping forces acting on the wall during its propagation. It is demonstrated that unidirectional effect in domain wall propagation can be strongly reduced by annealing the wire at temperatures higher than 350 °C.

Non-local damage rheology and size effect

NASA Astrophysics Data System (ADS)

Lyakhovsky, V.

2011-12-01

We study scaling relations controlling the onset of transiently-accelerating fracturing and transition to dynamic rupture propagation in a non-local damage rheology model. The size effect is caused principally by growth of a fracture process zone, involving stress redistribution and energy release associated with a large fracture. This implies that rupture nucleation and transition to dynamic propagation are inherently scale-dependent processes. Linear elastic fracture mechanics (LEFM) and local damage mechanics are formulated in terms of dimensionless strain components and thus do not allow introducing any space scaling, except linear relations between fracture length and displacements. Generalization of Weibull theory provides scaling relations between stress and crack length at the onset of failure. A powerful extension of the LEFM formulation is the displacement-weakening model which postulates that yielding is complete when the crack wall displacement exceeds some critical value or slip-weakening distance Dc at which a transition to kinetic friction is complete. Scaling relations controlling the transition to dynamic rupture propagation in slip-weakening formulation are widely accepted in earthquake physics. Strong micro-crack interaction in a process zone may be accounted for by adopting either integral or gradient type non-local damage models. We formulate a gradient-type model with free energy depending on the scalar damage parameter and its spatial derivative. The damage-gradient term leads to structural stresses in the constitutive stress-strain relations and a damage diffusion term in the kinetic equation for damage evolution. The damage diffusion eliminates the singular localization predicted by local models. The finite width of the localization zone provides a fundamental length scale that allows numerical simulations with the model to achieve the continuum limit. A diffusive term in the damage evolution gives rise to additional damage diffusive time scale associated with the structural length scale. The ratio between two time scales associated with damage accumulation and diffusion, the damage diffusivity ratio, reflects the role of the diffusion-controlled delocalization. We demonstrate that localized fracturing occurs at the damage diffusivity ratio below certain critical value leading to a linear scaling between stress and crack length compatible with size effect for failures at crack initiation. A subseuqent quasi-static fracture growth is self-similar with increasing size of the process zone proportional to the fracture length. At a certain stage, controlled by dynamic weakening, the self-similarity breaks down and crack velocity significantly deviates from that predicted by the quasi-static regime, the size of the process zone decreases, and the rate of crack growth ceases to be controlled by the rate of damage increase. Furthermore, the crack speed approaches that predicted by the elasto-dynamic equation. The non-local damage rheology model predicts that the nucleation size of the dynamic fracture scales with fault zone thickness distance of the stress interraction.

Numerical simulation and experimental validation of Lamb wave propagation behavior in composite plates

NASA Astrophysics Data System (ADS)

Kim, Sungwon; Uprety, Bibhisha; Mathews, V. John; Adams, Daniel O.

2015-03-01

Structural Health Monitoring (SHM) based on Acoustic Emission (AE) is dependent on both the sensors to detect an impact event as well as an algorithm to determine the impact location. The propagation of Lamb waves produced by an impact event in thin composite structures is affected by several unique aspects including material anisotropy, ply orientations, and geometric discontinuities within the structure. The development of accurate numerical models of Lamb wave propagation has important benefits towards the development of AE-based SHM systems for impact location estimation. Currently, many impact location algorithms utilize the time of arrival or velocities of Lamb waves. Therefore the numerical prediction of characteristic wave velocities is of great interest. Additionally, the propagation of the initial symmetric (S0) and asymmetric (A0) wave modes is important, as these wave modes are used for time of arrival estimation. In this investigation, finite element analyses were performed to investigate aspects of Lamb wave propagation in composite plates with active signal excitation. A comparative evaluation of two three-dimensional modeling approaches was performed, with emphasis placed on the propagation and velocity of both the S0 and A0 wave modes. Results from numerical simulations are compared to experimental results obtained from active AE testing. Of particular interest is the directional dependence of Lamb waves in quasi-isotropic carbon/epoxy composite plates. Numerical and experimental results suggest that although a quasi-isotropic composite plate may have the same effective elastic modulus in all in-plane directions, the Lamb wave velocity may have some directional dependence. Further numerical analyses were performed to investigate Lamb wave propagation associated with circular cutouts in composite plates.

The role of drop velocity in statistical spray description

NASA Technical Reports Server (NTRS)

Groeneweg, J. F.; El-Wakil, M. M.; Myers, P. S.; Uyehara, O. A.

1978-01-01

The justification for describing a spray by treating drop velocity as a random variable on an equal statistical basis with drop size was studied experimentally. A double exposure technique using fluorescent drop photography was used to make size and velocity measurements at selected locations in a steady ethanol spray formed by a swirl atomizer. The size velocity data were categorized to construct bivariate spray density functions to describe the spray immediately after formation and during downstream propagation. Bimodal density functions were formed by environmental interaction during downstream propagation. Large differences were also found between spatial mass density and mass flux size distribution at the same location.

Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission

PubMed Central

Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

2015-01-01

In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the “front” of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region. PMID:25631746

Wave propagation modelling of induced earthquakes at the Groningen gas production site

NASA Astrophysics Data System (ADS)

Paap, Bob; Kraaijpoel, Dirk; Bakker, Marcel; Gharti, Hom Nath

2018-06-01

Gas extraction from the Groningen natural gas field, situated in the Netherlands, frequently induces earthquakes in the reservoir that cause damage to buildings and pose a safety hazard and a nuisance to the local population. Due to the dependence of the national heating infrastructure on Groningen gas, the short-term mitigation measures are mostly limited to a combination of spatiotemporal redistribution of gas production and strengthening measures for buildings. All options become more effective with a better understanding of both source processes and seismic wave propagation. Detailed wave propagation simulations improve both the inference of source processes from observed ground motions and the forecast of ground motions as input for hazard studies and seismic network design. The velocity structure at the Groningen site is relatively complex, including both deep high-velocity and shallow low-velocity deposits showing significant thickness variations over relatively small spatial extents. We performed a detailed three-dimensional wave propagation modelling study for an induced earthquake in the Groningen natural gas field using the spectral-element method. We considered an earthquake that nucleated along a normal fault with local magnitude of {{{M}}_{{L}}} = 3. We created a dense mesh with element size varying from 12 to 96 m, and used a source frequency of 7 Hz, such that frequencies generated during the simulation were accurately sampled up to 10 Hz. The velocity/density model is constructed using a three-dimensional geological model of the area, including both deep high-velocity salt deposits overlying the source region and shallow low-velocity sediments present in a deep but narrow tunnel valley. The results show that the three-dimensional density/velocity model in the Groningen area clearly play a large role in the wave propagation and resulting surface ground motions. The 3d structure results in significant lateral variations in site response. The high-velocity salt deposits have a dispersive effect on the radiated wavefield, reducing the seismic energy reaching the surface near the epicentre. In turn, the presence of low-velocity tunnel valley deposits can locally cause a significant increase in peak ground acceleration. Here we study induced seismicity on a local scale and use SPECFEM3D to conduct full waveform simulations and show how local velocity variations can affect seismic records.

Comparison of Visual and Acoustic Emission Observations in a Four Point Bending Experiment on Barre Granite

NASA Astrophysics Data System (ADS)

Li, Bing Qiuyi; Einstein, Herbert H.

2017-09-01

We present an experimental study in which a pre-notched specimen of Barre Granite was subjected to four point bending under crack mouth opening displacement control. The experimental observations consisted of load-displacement measurements, acoustic emissions, and photography on a macroscopic ( cm) as well as microscopic ( μm) scale. These observations were compared and analysed to better understand process zone development and crack propagation. Load-displacement data showed that the load reaches its maximum at crack initiation, and the machine input work is constant while the crack propagates. AE moment magnitudes between Mw = -6 to -10 were observed, and focal mechanisms consisted of both shear and tensile components. During process zone development, AE formed a large cloud of events located near the notch tip and then tended to occur away from the notch tip as the crack propagated. Image analysis at the microscopic scale showed that microcracks formed and coalesced during process zone development; specifically, the microcracks initiated in tension and then propagated as a series of en-echelon cracks. In general, the synthesis of the three observations showed that a wider bulb of activity at lower energy tended to occur during process zone development, while crack propagation tended to be more spatially concentrated and contained higher energy.

Turbulence, combustion, pollutant, and stability characterization of a premixed, step combustor

NASA Technical Reports Server (NTRS)

Ganji, A. T.; Sawyer, R. F.

1980-01-01

A two dimensional combustion tunnel was constructed to study a lean premixed turbulent propane/air flame stablized behind a rearward facing step. Studied were: (1) the existence and importance of large coherent structures in turbulent reacting and nonreacting free shear layers behind the steps; (2) the effect of inlet temperature and reference velocity on combustion efficiency; (3) CO, NO2 and NO sub x production in the flame; and (4) the blowout and upstream propagation of the flame. In the ranges studied, the large coherent structures dominated both the reacting and the nonreacting free shear layers behind the step. The growth of the vortices and the propagation of the flamer were intimately linked. Vortex pairing was observed to be one of the mechanisms for introduction of fresh reactants into the shear layer and growth of the shear layer. Probe composition measurements of the flame showed that, in the recirculation zone, the reaction was above 99 percent complete, CO and unburnt hydrocarbons were above the equilibrium level NO sub x concentration was far below the equilibrium level and NO2 comprised a negligible fraction of NO sub x.

Extremal inversion of lunar travel time data. [seismic velocity structure

NASA Technical Reports Server (NTRS)

Burkhard, N.; Jackson, D. D.

1975-01-01

The tau method, developed by Bessonova et al. (1974), of inversion of travel times is applied to lunar P-wave travel time data to find limits on the velocity structure of the moon. Tau is the singular solution to the Clairaut equation. Models with low-velocity zones, with low-velocity zones at differing depths, and without low-velocity zones, were found to be consistent with data and within the determined limits. Models with and without a discontinuity at about 25-km depth have been found which agree with all travel time data to within two standard deviations. In other words, the existence of the discontinuity and its size and location have not been uniquely resolved. Models with low-velocity channels are also possible.

An experiment to measure the one-way velocity of propagation of electromagnetic radiation

NASA Technical Reports Server (NTRS)

Kolen, P.; Torr, D. G.

1982-01-01

An experiment involving commercially available instrumentation to measure the velocity of the earth with respect to absolute space is described. The experiment involves the measurement of the one-way propagation velocity of electromagnetic radiation down a high-quality coaxial cable. It is demonstrated that the experiment is both physically meaningful and exceedingly simple in concept and in implementation. It is shown that with currently available commercial equipment one might expect to detect a threshold value for the component of velocity of the earth's motion with respect to absolute space in the equatorial plane of approximately 10 km/s, which greatly exceeds the velocity resolution required to detect the motion of the solar system with respect to the center of the galaxy.

The Universal Role of Tubulence in the Propagation of Strong Shocks and Detonation Waves

NASA Astrophysics Data System (ADS)

Lee, John H.

2001-06-01

The passage of a strong shock wave usually results in irreversible physical and chemical changes in the medium. If the chemical reactions are sufficiently exothermic, the shock wave can be self-propagating, i.e., sustained by the chemical energy release via the expansion work of the reaction products. Although shocks and detonations can be globally stable and propagate at constant velocities (in the direction of motion), their structure may be highly unstable and exhibit large hydrodynamic fluctuations, i.e., turbulence. Recent investigations on plastic deformation of polycrystalline material behind shock waves have revealed particle velocity dispersion at the mesoscopic level, a result of vortical rotational motion similar to that of turbulent fluid flows at high Reynolds number.1 Strong ionizing shocks in noble gases2, as well as dissociating shock waves in carbon dioxide,3 also demonstrate a turbulent density fluctuation in the non-equilibrium shock transition zone. Perhaps the most thoroughly investigated unstable structure is that of detonation waves in gaseous explosives.4 Detonation waves in liquid explosives such as nitromethane also take on similar unstable structure as gaseous detonations.5 There are also indications that detonations in solid explosives have a similar unsteady structure under certain conditions. Thus, it appears that it is more of a rule than an exception that the structure of strong shocks and detonations are unstable and exhibit turbulent-like fluctuations as improved diagnostics now permit us to look more closely at the meso- and micro-levels. Increasing attention is now devoted to the understanding of the shock waves at the micro-scale level in recent years. This is motivated by the need to formulate physical and chemical models that contain the correct physics capable of describing quantitatively the shock transition process. It should be noted that, in spite of its unstable 3-D structure, the steady 1-D conservation laws (in the direction of propagation) apply across the shock transition zone if the downstream equilibrium plane is taken far enough away to ensure the decay of the turbulent fluctuations. Thus, the Hugoniot properties of one-dimensional propagation of shock and detonation waves remain valid. However, the conservation laws do not describe the important propagation mechanisms (i.e., the physical and chemical processes that effect the transition from initial to the final state) in the wave structure. Since gaseous detonations enjoy the advantage of being able to be observed experimentally in great detail, its complex turbulent structure is now quite well established. Furthermore, the equation of state for perfect gases is well known and the chemistry of most gas phase reactions is also sufficiently understood quantitatively to permit detailed numerical simulation of the complex detonation structure. Thus, a good database of information exists for gaseous detonation, and in this paper we shall explore the turbulent structure of gaseous detonation with the aim of answering the question as to "why nature prefers to evoke such a complicated manner to effect its propagation." We will then attempt to generalize the discussion to the "terra incognita" of condensed phase materials where the structure is much less understood. 1. Meshcheryakov, Yu.I., and Atroshenko, S.A., Izv. Vyssh. Uchebn. Zaved. Fiz., 4, 105-123 (1992). 2. Glass, I.I, and Liu, W.S., J. Fluid Mech., 84(1), 55-77 (1978). 3. Griffiths, R.W., Sanderman, R.J., and Hornung, H.G., J. Phys. D., 8, 1681-1691 (1975). 4. Lee, J.H.S., Ann. Rev. Fluid Mech., 16, 311-336 (1984). 5. Mallory, H.D., J. Appl. Physics, 38, 5302-5306 (1967).

Moment tensor inversion of the 2016 southeast offshore Mie earthquake in the Tonankai region using a three-dimensional velocity structure model: effects of the accretionary prism and subducting oceanic plate

NASA Astrophysics Data System (ADS)

Takemura, Shunsuke; Kimura, Takeshi; Saito, Tatsuhiko; Kubo, Hisahiko; Shiomi, Katsuhiko

2018-03-01

The southeast offshore Mie earthquake occurred on April 1, 2016 near the rupture area of the 1944 Tonankai earthquake, where seismicity around the interface of the Philippine Sea plate had been very low until this earthquake. Since this earthquake occurred outside of seismic arrays, the focal mechanism and depth were not precisely constrained using a one-dimensional velocity model, as in a conventional approach. We conducted a moment tensor inversion of this earthquake by using a three-dimensional velocity structure model. Before the analysis of observed data, we investigated the effects of offshore heterogeneous structures such as the seawater, accretionary prism, and subducting oceanic plate by using synthetic seismograms in a full three-dimensional model and simpler models. The accretionary prism and subducting oceanic plate play important roles in the moment tensor inversion for offshore earthquakes in the subduction zone. Particularly, the accretionary prism, which controls the excitation and propagation of long-period surface waves around the offshore region, provides better estimations of the centroid depths and focal mechanisms of earthquakes around the Nankai subduction zone. The result of moment tensor inversion for the 2016 southeast offshore Mie earthquake revealed low-angle thrust faulting with a moment magnitude of 5.6. According to geophysical surveys in the Nankai Trough, our results suggest that the rupture of this earthquake occurred on the interface of the Philippine Sea plate, rather than on a mega-splay fault. Detailed comparisons of first-motion polarizations provided additional constraints of the rupture that occurred on the interface of the Philippine Sea plate.

High resolution crustal image of South California Continental Borderland: Reverse time imaging including multiples

NASA Astrophysics Data System (ADS)

Bian, A.; Gantela, C.

2014-12-01

Strong multiples were observed in marine seismic data of Los Angeles Regional Seismic Experiment (LARSE).It is crucial to eliminate these multiples in conventional ray-based or one-way wave-equation based depth image methods. As long as multiples contain information of target zone along travelling path, it's possible to use them as signal, to improve the illumination coverage thus enhance the image quality of structural boundaries. Reverse time migration including multiples is a two-way wave-equation based prestack depth image method that uses both primaries and multiples to map structural boundaries. Several factors, including source wavelet, velocity model, back ground noise, data acquisition geometry and preprocessing workflow may influence the quality of image. The source wavelet is estimated from direct arrival of marine seismic data. Migration velocity model is derived from integrated model building workflow, and the sharp velocity interfaces near sea bottom needs to be preserved in order to generate multiples in the forward and backward propagation steps. The strong amplitude, low frequency marine back ground noise needs to be removed before the final imaging process. High resolution reverse time image sections of LARSE Lines 1 and Line 2 show five interfaces: depth of sea-bottom, base of sedimentary basins, top of Catalina Schist, a deep layer and a possible pluton boundary. Catalina Schist shows highs in the San Clemente ridge, Emery Knoll, Catalina Ridge, under Catalina Basin on both the lines, and a minor high under Avalon Knoll. The high of anticlinal fold in Line 1 is under the north edge of Emery Knoll and under the San Clemente fault zone. An area devoid of any reflection features are interpreted as sides of an igneous plume.

Migration of dispersive GPR data

USGS Publications Warehouse

Powers, M.H.; Oden, C.P.; ,

2004-01-01

Electrical conductivity and dielectric and magnetic relaxation phenomena cause electromagnetic propagation to be dispersive in earth materials. Both velocity and attenuation may vary with frequency, depending on the frequency content of the propagating energy and the nature of the relaxation phenomena. A minor amount of velocity dispersion is associated with high attenuation. For this reason, measuring effects of velocity dispersion in ground penetrating radar (GPR) data is difficult. With a dispersive forward model, GPR responses to propagation through materials with known frequency-dependent properties have been created. These responses are used as test data for migration algorithms that have been modified to handle specific aspects of dispersive media. When either Stolt or Gazdag migration methods are modified to correct for just velocity dispersion, the results are little changed from standard migration. For nondispersive propagating wavefield data, like deep seismic, ensuring correct phase summation in a migration algorithm is more important than correctly handling amplitude. However, the results of migrating model responses to dispersive media with modified algorithms indicate that, in this case, correcting for frequency-dependent amplitude loss has a much greater effect on the result than correcting for proper phase summation. A modified migration is only effective when it includes attenuation recovery, performing deconvolution and migration simultaneously.

On the propagation of hydromagnetic waves in a plasma of thermal and suprathermal components

NASA Astrophysics Data System (ADS)

Kumar, Nagendra; Sikka, Himanshu

2007-12-01

The propagation of MHD waves is studied when two ideal fluids, thermal and suprathermal gases, coupled by magnetic field are moving with the steady flow velocity. The fluids move independently in a direction perpendicular to the magnetic field but gets coupled along the field. Due to the presence of flow in suprathermal and thermal fluids there appears forward and backward waves. All the forward and backward modes propagate in such a way that their rate of change of phase speed with the thermal Mach number is same. It is also found that besides the usual hydromagnetic modes there appears a suprathermal mode which propagates with faster speed. Surface waves are also examined on an interface formed with composite plasma (suprathermal and thermal gases) on one side and the other is a non-magnetized plasma. In this case, the modes obtained are two or three depending on whether the sound velocity in thermal gas is equal to or greater than the sound velocity in suprathermal gas. The results lead to the conclusion that the interaction of thermal and suprathermal components may lead to the occurrence of an additional mode called suprathermal mode whose phase velocity is higher than all the other modes.

Does velocity-strengthening to velocity-weakening transition really determine the updip limit of the seismogenic zone in subduction megathrusts?

NASA Astrophysics Data System (ADS)

Shimamoto, T.

2009-12-01

Understanding the mechanisms of thrust-type earthquakes in subduction zones is the primary target of seismogenic-zone drilling project in Nankai Trough. Drilling into the upper part of the seismogenic zone is attempted, so that understanding the processes controlling the updip limit of the seismogenic zone is becoming a more specific target. A commonly accepted notion is that the onset of seismic behavior is due to a change in velocity strengthening to velocity weakening property of fault zone (see Saffer & Marone, 2003, EPSL ). Smectite-illite transformation had been a fashionable hypothesis for such a transition because the transformation is likely to occur near the updip limit of the seismogenic zone. However, Saffer & Marone recognized velocity-strengthening behavior of illite gouge questioning the smectite-illite transformation as the primary cause for the updip limit of seismic zone. They explored other possibilities that might cause a change in the velocity dependency of friction. I want to address the problem from a different angle. Progress in high-velocity friction in the last 15 years has demonstrated that nearly all faults exhibit dramatic weakening at high slip rates and large displacements. The weakening is indeed greater than the changes in friction at slow slip rates by more than one order of magnitude, and the slip- and velocity-weakening of faults at high velocities is likely to control the dynamic fault motion during large earthquakes. Thus by combining abundant work on rate-and-state dependent friction at slow slip rates and recent high-velocity friction studies, a possibility emerges in that the rate-and-state friction at slow slip rates controls the earthquake nucleation, whereas intermediate to high-velocity friction dictates the growth processes into a large earthquake. Taiwan Chi-Chi earthquake in 1999 is very interesting in this regard because Tanikawa & Shimamoto (2008, JGR ) recognized velocity-strengthening properties for gouge from the northern part of the Chelungpu fault (velocity weakening for gouge from the south). The northern part of the fault should be aseismic according to a traditional view for earthquakes in velocity-weakening regime, whereas the northern part displaced much more at higher slip rates with lower frequencies than in southern part. Permeability of fault gouge is lower in the north than in the south by one to two orders of magnitude, so that high-velocity weakening is more pronounced in the north due to more effective thermal pressurization than in the south. Thus Tanikawa & Shimamoto proposed a scenario that the Chi-Chi earthquake started from the southern part of Chelungpu fault with velocity-weakening property and that the earthquake rupture grew more in the north due to high-velocity weakening. Noda & Lapusta (2009, JPGU meeting ) demonstrated by dynamic modeling that such a scenario is indeed possible. I propose that such a scenario is applicable to shallow subduction zone where earthquake rupture comes from deeper parts. This change in view will change the scope of laboratory work, modeling, and even ways of looking at faults in accretionary prism such as Shimanto belt. Those problems will be elaborated in my presentation.

Imaging of Fine Shallow Structure Beneath the Longmenshan Fault Zone from Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Zhao, P.; Campillo, M.; Chen, J.; Liu, Q.

2016-12-01

Short period seismic ambient noise group velocity dispersion curve, obtained from cross correlation of vertical component of 57 stations around the Longmenshan fault zone deployed after the Wenchuan earthquake and continuously observed for 1 year, is used to inverse the S wave velocity structure of the top 25 km of the central to northern part of Longmenshan fault zone. A iterative correction method based on 3-D simulation is proposed to reduce the influence of elevation. After 7 times of correction, a fine shllow S-wave velocity structure comes out. The results show that (1) Velocity structure above 10 km keeps good consistency with the surface fault system around Longmenshan, and controls the deep extension features of most major faults. Below the depth of 15 km, the velocity structure presents cross tectonic frame work along both Longmenshan and Minshan. The complex structure may have affected the rupture process of the Wenchuan earthquake. (2) The depth velocity structure profiles give good constraint for the deep geometry of main faults. The characteristics of the high angle, listric, reverse structure of the Longmenshan faults is further confirmed by our results.(3) At southern part of the study area, low-velocity structure is found at about 20km depth beneath the Pengguan massif, which is related to the low velocity layer in the middle crust of Songpan-Ganzi block. This may be an evidence for the existence of brittle-ductile transition zone in southern part of the rupture zone of the Wenchuan earthquake at the depth around 22km. Our results show the great potential of short period ambient noise tomography with data from densepassive seismic array in the study of fine velocity structure and fault zone imaging.

Internal dynamics of a free-surface viscoplastic flow down an inclined plane: experimental results through PIV measurements

NASA Astrophysics Data System (ADS)

Freydier, Perrine; Chambon, Guillaume; Naaim, Mohamed

2015-04-01

Debris flows constitute one of the most important natural hazards throughout the mountainous regions of the world, causing significant damages and economic losses. These mass are composed of particles of all sizes from clay to boulders suspended in a viscous fluid. An important goal resides in developing models that are able to accurately predict the hydraulic properties of debris flows. First, these flows are generally represented using models based on a momentum integral approach that consists in assuming a shallow flow and in depth averaging the local conservation equations. These models take into account closure terms depending on the shape of the velocity profile inside the flow. Second, the specific migration mechanisms of the suspended particles, which have a strong influence on the propagation of the surges, also depend on the internal dynamics within the flow. However, to date, few studies concerning the internal dynamics in particular in the vicinity of the front, of such flows have been carried out. The aim of this study is to document the internal dynamics in free-surface viscoplastic flows down an inclined channel. The rheological studies concerning natural muddy debris flows, rich in fine particles, have shown that these materials can be modeled, at least as a first approximation as non-Newtonian viscoplastic fluids. Experiments are conducted in an inclined channel whose bottom is constituted by an upward-moving conveyor belt with controlled velocity. Carbopol microgel has been used as a homogeneous transparent viscoplastic fluid. This experimental setup allows generating and monitoring stationary gravity-driven surges in the laboratory frame. We use PIV technique (Particle Image Velocimetry) to obtain velocity fields both in the uniform zone and within the front zone where flow thickness is variable and where recirculation takes place. Experimental velocity profiles and determination of plug position will be presented and compared to theoretical predictions based on lubrication approximation.

Characterization of Carbonate Hydrostratigraphy Using Ambient Seismic Noise: A Pilot Study in the Floridan Aquifer System, Ocala, FL, USA

NASA Astrophysics Data System (ADS)

James, S.; Screaton, E.; Russo, R. M.; Panning, M. P.; Bremner, P. M.; Stanciu, A. C.; Torpey, M. E.; Hongsresawat, S.; Farrell, M. E.

2014-12-01

Defining zones of high and low hydraulic conductivity within aquifers is vital to hydrogeologic research and groundwater management. Carbonate aquifers are particularly difficult to characterize due to dissolution and dolomitization. We investigated a new imaging technique for aquifer characterization that uses cross-correlation of ambient seismic noise to determine seismic velocity structure. Differences in densities between confining units and high permeability flow zones can produce distinct seismic velocities in the correlated signals. We deployed an array of 9 short period geophones from 11/2013 to 3/2014 in Indian Lake State Forest, Florida, to determine if the high frequency diffusive seismic wavefield can be used for imaging hydrostratigraphy. Here, a thin surficial layer of siliciclastic deposits overlie a ~ 0.6 km sequence of Cenozoic limestone and dolomite units that comprise the Floridan Aquifer System (FAS). A low permeability dolomite unit vertically divides the FAS throughout most of Florida. Deep boreholes surrounding the site constrain hydrostratigraphy, however the horizontal continuity of the middle dolomite unit as well as its effectiveness as a confining unit in the study area are not well known. The stations were spaced at distances ranging from 0.18 to 2.6 km, and yielded 72 cross-correlation Green's functions for Rayleigh wave propagation at frequencies between 0.2 and 40 Hz, with dominant peaks around 0.8 Hz, 3 Hz and 13 Hz. Local vehicle traffic did interfere to a degree with the correlation of the diffuse waves, but was minimized by using only nighttime data. At the lowest frequencies (greatest depths) investigated, velocities increase with depth; however, correlations become less coherent at higher frequencies, perhaps due to shallow complex scattering. Comparison of cross-correlations for all station pairs also indicates spatial variations in velocity. Thus, the method shows promise for characterization of the heterogeneity of the Floridan Aquifer System.

Ultrasonic wave velocity measurement in small polymeric and cortical bone specimens

NASA Technical Reports Server (NTRS)

Kohles, S. S.; Bowers, J. R.; Vailas, A. C.; Vanderby, R. Jr

1997-01-01

A system was refined for the determination of the bulk ultrasonic wave propagation velocity in small cortical bone specimens. Longitudinal and shear wave propagations were measured using ceramic, piezoelectric 20 and 5 MHz transducers, respectively. Results of the pulse transmission technique were refined via the measurement of the system delay time. The precision and accuracy of the system were quantified using small specimens of polyoxymethylene, polystyrene-butadiene, and high-density polyethylene. These polymeric materials had known acoustic properties, similarity of propagation velocities to cortical bone, and minimal sample inhomogeneity. Dependence of longitudinal and transverse specimen dimensions upon propagation times was quantified. To confirm the consistency of longitudinal wave propagation in small cortical bone specimens (< 1.0 mm), cut-down specimens were prepared from a normal rat femur. Finally, cortical samples were prepared from each of ten normal rat femora, and Young's moduli (Eii), shear moduli (Gij), and Poisson ratios (Vij) were measured. For all specimens (bone, polyoxymethylene, polystyrene-butadiene, and high-density polyethylene), strong linear correlations (R2 > 0.997) were maintained between propagation time and distance throughout the size ranges down to less than 0.4 mm. Results for polyoxymethylene, polystyrene-butadiene, and high-density polyethylene were accurate to within 5 percent of reported literature values. Measurement repeatability (precision) improved with an increase in the wave transmission distance (propagating dimension). No statistically significant effect due to the transverse dimension was detected.

Comparative velocity structure of active Hawaiian volcanoes from 3-D onshore-offshore seismic tomography

USGS Publications Warehouse

Park, J.; Morgan, J.K.; Zelt, C.A.; Okubo, P.G.; Peters, L.; Benesh, N.

2007-01-01

We present a 3-D P-wave velocity model of the combined subaerial and submarine portions of the southeastern part of the Island of Hawaii, based on first-arrival seismic tomography of marine airgun shots recorded by the onland seismic network. Our model shows that high-velocity materials (6.5-7.0??km/s) lie beneath Kilauea's summit, Koae fault zone, and the upper Southwest Rift Zone (SWRZ) and upper and middle East Rift Zone (ERZ), indicative of magma cumulates within the volcanic edifice. A separate high-velocity body of 6.5-6.9??km/s within Kilauea's lower ERZ and upper Puna Ridge suggests a distinct body of magma cumulates, possibly connected to the summit magma cumulates at depth. The two cumulate bodies within Kilauea's ERZ may have undergone separate ductile flow seaward, influencing the submarine morphology of Kilauea's south flank. Low velocities (5.0-6.3??km/s) seaward of Kilauea's Hilina fault zone, and along Mauna Loa's seaward facing Kao'iki fault zone, are attributed to thick piles of volcaniclastic sediments deposited on the submarine flanks. Loihi seamount shows high-velocity anomalies beneath the summit and along the rift zones, similar to the interpreted magma cumulates below Mauna Loa and Kilauea volcanoes, and a low-velocity anomaly beneath the oceanic crust, probably indicative of melt within the upper mantle. Around Kilauea's submarine flank, a high-velocity anomaly beneath the outer bench suggests the presence of an ancient seamount that may obstruct outward spreading of the flank. Mauna Loa's southeast flank is also marked by a large, anomalously high-velocity feature (7.0-7.4??km/s), interpreted to define an inactive, buried volcanic rift zone, which might provide a new explanation for the westward migration of Mauna Loa's current SWRZ and the growth of Kilauea's SWRZ. ?? 2007 Elsevier B.V. All rights reserved.

Study on 3-D velocity structure of crust and upper mantle in Sichuan-yunnan region, China

USGS Publications Warehouse

Wang, C.; Mooney, W.D.; Wang, X.; Wu, J.; Lou, H.; Wang, F.

2002-01-01

Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others appear the characteristic of tectonic boundary, indicating that the faults litely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the Sichuan-Yunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the Indian and the Asian plates. The crustal velocity in the Sichuan-Yunnan rhombic block generally shows normal.value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below.

Crustal structure and kinematics of the TAMMAR propagating rift system on the Mid-Atlantic Ridge from seismic refraction and satellite altimetry gravity

NASA Astrophysics Data System (ADS)

Kahle, Richard L.; Tilmann, Frederik; Grevemeyer, Ingo

2016-08-01

The TAMMAR segment of the Mid-Atlantic Ridge forms a classic propagating system centred about two degrees south of the Kane Fracture Zone. The segment is propagating to the south at a rate of 14 mm yr-1, 15 per cent faster than the half-spreading rate. Here, we use seismic refraction data across the propagating rift, sheared zone and failed rift to investigate the crustal structure of the system. Inversion of the seismic data agrees remarkably well with crustal thicknesses determined from gravity modelling. We show that the crust is thickened beneath the highly magmatic propagating rift, reaching a maximum thickness of almost 8 km along the seismic line and an inferred (from gravity) thickness of about 9 km at its centre. In contrast, the crust in the sheared zone is mostly 4.5-6.5 km thick, averaging over 1 km thinner than normal oceanic crust, and reaching a minimum thickness of only 3.5 km in its NW corner. Along the seismic line, it reaches a minimum thickness of under 5 km. The PmP reflection beneath the sheared zone and failed rift is very weak or absent, suggesting serpentinisation beneath the Moho, and thus effective transport of water through the sheared zone crust. We ascribe this increased porosity in the sheared zone to extensive fracturing and faulting during deformation. We show that a bookshelf-faulting kinematic model predicts significantly more crustal thinning than is observed, suggesting that an additional mechanism of deformation is required. We therefore propose that deformation is partitioned between bookshelf faulting and simple shear, with no more than 60 per cent taken up by bookshelf faulting.

Analytic Study of Three-Dimensional Rupture Propagation in Strike-Slip Faulting with Analogue Models

NASA Astrophysics Data System (ADS)

Chan, Pei-Chen; Chu, Sheng-Shin; Lin, Ming-Lang

2014-05-01

Strike-slip faults are high angle (or nearly vertical) fractures where the blocks have moved along strike way (nearly horizontal). Overburden soil profiles across main faults of Strike-slip faults have revealed the palm and tulip structure characteristics. McCalpin (2005) has trace rupture propagation on overburden soil surface. In this study, we used different offset of slip sandbox model profiles to study the evolution of three-dimensional rupture propagation by strike -slip faulting. In strike-slip faults model, type of rupture propagation and width of shear zone (W) are primary affecting by depth of overburden layer (H), distances of fault slip (Sy). There are few research to trace of three-dimensional rupture behavior and propagation. Therefore, in this simplified sandbox model, investigate rupture propagation and shear zone with profiles across main faults when formation are affecting by depth of overburden layer and distances of fault slip. The investigators at the model included width of shear zone, length of rupture (L), angle of rupture (θ) and space of rupture. The surface results was follow the literature that the evolution sequence of failure envelope was R-faults, P-faults and Y-faults which are parallel to the basement fault. Comparison surface and profiles structure which were curved faces and cross each other to define 3-D rupture and width of shear zone. We found that an increase in fault slip could result in a greater width of shear zone, and proposed a W/H versus Sy/H relationship. Deformation of shear zone showed a similar trend as in the literature that the increase of fault slip resulted in the increase of W, however, the increasing trend became opposite after a peak (when Sy/H was 1) value of W was reached (small than 1.5). The results showed that the W width is limited at a constant value in 3-D models by strike-slip faulting. In conclusion, this study helps evaluate the extensions of the shear zone influenced regions for strike-slip faults.

Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California

USGS Publications Warehouse

Li, Y.-G.; Ellsworth, W.L.; Thurber, C.H.; Malin, P.E.; Aki, K.

1997-01-01

Fault-zone guided waves were successfully excited by near-surface explosions in the San Andreas fault zone both at Parkfield and Cienega Valley, central California. The guided waves were observed on linear, three-component seismic arrays deployed across the fault trace. These waves were not excited by explosions located outside the fault zone. The amplitude spectra of guided waves show a maximum peak at 2 Hz at Parkfield and 3 Hz at Cienega Valley. The guided wave amplitude decays sharply with observation distance from the fault trace. The explosion-excited fault-zone guided waves are similar to those generated by earthquakes at Parkfield but have lower frequencies and travel more slowly. These observations suggest that the fault-zone wave guide has lower seismic velocities as it approaches the surface at Parkfield. We have modeled the waveforms as S waves trapped in a low-velocity wave guide sandwiched between high-velocity wall rocks, resulting in Love-type fault-zone guided waves. While the results are nonunique, the Parkfield data are adequately fit by a shallow wave guide 170 m wide with an S velocity 0.85 km/sec and an apparent Q ??? 30 to 40. At Cienega Valley, the fault-zone wave guide appears to be about 120 m wide with an S velocity 0.7 km/sec and a Q ??? 30.

Finite-Source Inversion for the 2004 Parkfield Earthquake using 3D Velocity Model Green's Functions

NASA Astrophysics Data System (ADS)

Kim, A.; Dreger, D.; Larsen, S.

2008-12-01

We determine finite fault models of the 2004 Parkfield earthquake using 3D Green's functions. Because of the dense station coverage and detailed 3D velocity structure model in this region, this earthquake provides an excellent opportunity to examine how the 3D velocity structure affects the finite fault inverse solutions. Various studies (e.g. Michaels and Eberhart-Phillips, 1991; Thurber et al., 2006) indicate that there is a pronounced velocity contrast across the San Andreas Fault along the Parkfield segment. Also the fault zone at Parkfield is wide as evidenced by mapped surface faults and where surface slip and creep occurred in the 1966 and the 2004 Parkfield earthquakes. For high resolution images of the rupture process"Ait is necessary to include the accurate 3D velocity structure for the finite source inversion. Liu and Aurchuleta (2004) performed finite fault inversions using both 1D and 3D Green's functions for 1989 Loma Prieta earthquake using the same source paramerization and data but different Green's functions and found that the models were quite different. This indicates that the choice of the velocity model significantly affects the waveform modeling at near-fault stations. In this study, we used the P-wave velocity model developed by Thurber et al (2006) to construct the 3D Green's functions. P-wave speeds are converted to S-wave speeds and density using by the empirical relationships of Brocher (2005). Using a finite difference method, E3D (Larsen and Schultz, 1995), we computed the 3D Green's functions numerically by inserting body forces at each station. Using reciprocity, these Green's functions are recombined to represent the ground motion at each station due to the slip on the fault plane. First we modeled the waveforms of small earthquakes to validate the 3D velocity model and the reciprocity of the Green"fs function. In the numerical tests we found that the 3D velocity model predicted the individual phases well at frequencies lower than 0.25 Hz but that the velocity model is fast at stations located very close to the fault. In this near-fault zone the model also underpredicts the amplitudes. This implies the need to include an additional low velocity zone in the fault zone to fit the data. For the finite fault modeling we use the same stations as in our previous study (Kim and Dreger 2008), and compare the results to investigate the effect of 3D Green's functions on kinematic source inversions. References: Brocher, T. M., (2005), Empirical relations between elastic wavespeeds and density in the Earth's crust, Bull. Seism. Soc. Am., 95, No. 6, 2081-2092. Eberhart-Phillips, D., and A.J. Michael, (1993), Three-dimensional velocity structure and seismicity in the Parkfield region, central California, J. Geophys. Res., 98, 15,737-15,758. Kim A., D. S. Dreger (2008), Rupture process of the 2004 Parkfield earthquake from near-fault seismic waveform and geodetic records, J. Geophys. Res., 113, B07308. Thurber, C., H. Zhang, F. Waldhauser, J. Hardebeck, A. Michaels, and D. Eberhart-Phillips (2006), Three- dimensional compressional wavespeed model, earthquake relocations, and focal mechanisms for the Parkfield, California, region, Bull. Seism. Soc. Am., 96, S38-S49. Larsen, S., and C. A. Schultz (1995), ELAS3D: 2D/3D elastic finite-difference wave propagation code, Technical Report No. UCRL-MA-121792, 19pp. Liu, P., and R. J. Archuleta (2004), A new nonlinear finite fault inversion with three-dimensional Green's functions: Application to the 1989 Loma Prieta, California, earthquake, J. Geophys. Res., 109, B02318.

Thermal and viscous effects on sound waves: revised classical theory.

PubMed

Davis, Anthony M J; Brenner, Howard

2012-11-01

In this paper the recently developed, bi-velocity model of fluid mechanics based on the principles of linear irreversible thermodynamics (LIT) is applied to sound propagation in gases taking account of first-order thermal and viscous dissipation effects. The results are compared and contrasted with the classical Navier-Stokes-Fourier results of Pierce for this same situation cited in his textbook. Comparisons are also made with the recent analyses of Dadzie and Reese, whose molecularly based sound propagation calculations furnish results virtually identical with the purely macroscopic LIT-based bi-velocity results below, as well as being well-supported by experimental data. Illustrative dissipative sound propagation examples involving application of the bi-velocity model to several elementary situations are also provided, showing the disjoint entropy mode and the additional, evanescent viscous mode.

Reconciling deep seismic refraction and reflection data from the grenvillian-appalachian boundary in western New England

USGS Publications Warehouse

Hughes, S.; Luetgert, J.H.; Christensen, N.I.

1993-01-01

The Grenvillian-Appalachian boundary is characterized by pervasive mylonitic deformation and retrograde alteration of a suite of imbricated allochthonous and parautochthonous gneisses that were thrust upon the Grenvillian continental margin during the lower Paleozoic. Seismic reflection profiling across this structural boundary zone reveals prominent dipping reflectors interpreted as overthrust basement slices (parautochthons) of the Green Mountain Anticlinorium. In contrast, a seismic refraction study of the Grenvillian-Appalachian boundary reveals a sub-horizontally layered seismic velocity model that is difficult to reconcile with the pronounced sub-vertical structures observed in the Green mountains. A suite of rock samples was collected from the Green Mountain Anticlinorium and measured at high pressures in the laboratory to determine the seismic properties of these allochthonous and parautochthonous gneisses. The laboratory-measured seismic velocities agree favorably with the modelled velocity structure across the Grenvillian-Appalachian boundary suggesting that the rock samples are reliable indicators of the rock mass as whole. Samples of the parautochthonous Grenvillian basement exposed in the Green Mountains have lower velocities, by about 0.5 km/s, than lithologically equivalent units exposed in the eastern Adirondack Highlands. Velocity reduction in the Green Mountain parautochthons can be accounted for by retrograde metamorphic alteration (hydration) of the paragneisses. Seismic anisotropies, ranging from 2 to 12%, in the mylonitized Green Mountain paragneisses may also contribute to the observation of lower seismic velocities, where the direction of ray propagation is normal to the foliation. The velocity properties of the Green Mountain paragneisses are thus insufficiently different from the mantling Appalachian allochthons to permit their resolution by the Ontario-New York-New England seismic refraction profile. ?? 1993.

Eikonal Tomography of the Southern California Plate Boundary Region

NASA Astrophysics Data System (ADS)

Qiu, H.; Ben-Zion, Y.; Zigone, D.; Lin, F. C.

2016-12-01

We use eikonal tomography to derive directionally-dependent phase velocities of surface waves for the plate boundary region in southern CA sensitive to the approximate depth range 1-20 km. Seismic noise data recorded by 346 stations in the area provide a spatial coverage with 5-25 km typical station spacing and period range of 1-20 s. Noise cross-correlations are calculated for vertical component data recorded in year 2014. Rayleigh wave group and phase travel times between 2 and 13 sec period are derived for each station pair using frequency-time analysis. For each common station, all available phase travel time measurements with sufficient signal to noise ratio and envelope peak amplitude are used to construct a travel time map for a virtual source at the common station location. By solving the eikonal equation, both phase velocity and propagation direction are evaluated at each location for each virtual source. Isotropic phase velocities and 2-psi azimuthal anisotropy and their uncertainties are determined statistically using measurements from different virtual sources. Following the method of Barmin et al. (2001), group velocities are also inverted using all the group travel times that pass quality criteria. The obtained group and phase dispersions of Rayleigh waves are then inverted on a 6 x 6 km2 grid for local 1D piecewise shear wave velocity structures using the procedure of Herrmann (2013). The results agree well with previous observations of Zigone et al. (2015) in the overlapping area. Clear velocity contrasts and low velocity zones are seen for the San Andreas, San Jacinto, Elsinore and Garlock faults. We also find 2-psi azimuthal anisotropy with fast directions parallel to geometrically-simple fault sections. Details and updated results will be presented in the meeting.

A thermodynamic analysis of propagating subcritical cracks with cohesive zones

NASA Technical Reports Server (NTRS)

Allen, David H.

1993-01-01

The results of the so-called energetic approach to fracture with particular attention to the issue of energy dissipation due to crack propagation are applied to the case of a crack with cohesive zone. The thermodynamic admissibility of subcritical crack growth (SCG) is discussed together with some hypotheses that lead to the derivation of SCG laws. A two-phase cohesive zone model for discontinuous crack growth is presented and its thermodynamics analyzed, followed by an example of its possible application.

Velocity mode transition of dynamic crack propagation in hyperviscoelastic materials: A continuum model study

PubMed Central

Kubo, Atsushi; Umeno, Yoshitaka

2017-01-01

Experiments of crack propagation in rubbers have shown that a discontinuous jump of crack propagation velocity can occur as energy release rate increases, which is known as the “mode transition” phenomenon. Although it is believed that the mode transition is strongly related to the mechanical properties, the nature of the mode transition had not been revealed. In this study, dynamic crack propagation on an elastomer was investigated using the finite element method (FEM) with a hyperviscoelastic material model. A series of pure shear test was carried out numerically with FEM simulations and crack velocities were measured under various values of tensile strain. As a result, our FEM simulations successfully reproduced the mode transition. The success of realising the mode transition phenomenon by a simple FEM model, which was achieved for the first time ever, helped to explain that the phenomenon occurs owing to a characteristic non-monotonic temporal development of principal stress near the crack tip. PMID:28186205

Velocity mode transition of dynamic crack propagation in hyperviscoelastic materials: A continuum model study

NASA Astrophysics Data System (ADS)

Kubo, Atsushi; Umeno, Yoshitaka

2017-02-01

Experiments of crack propagation in rubbers have shown that a discontinuous jump of crack propagation velocity can occur as energy release rate increases, which is known as the “mode transition” phenomenon. Although it is believed that the mode transition is strongly related to the mechanical properties, the nature of the mode transition had not been revealed. In this study, dynamic crack propagation on an elastomer was investigated using the finite element method (FEM) with a hyperviscoelastic material model. A series of pure shear test was carried out numerically with FEM simulations and crack velocities were measured under various values of tensile strain. As a result, our FEM simulations successfully reproduced the mode transition. The success of realising the mode transition phenomenon by a simple FEM model, which was achieved for the first time ever, helped to explain that the phenomenon occurs owing to a characteristic non-monotonic temporal development of principal stress near the crack tip.

Velocity mode transition of dynamic crack propagation in hyperviscoelastic materials: A continuum model study.

PubMed

Kubo, Atsushi; Umeno, Yoshitaka

2017-02-10

Experiments of crack propagation in rubbers have shown that a discontinuous jump of crack propagation velocity can occur as energy release rate increases, which is known as the "mode transition" phenomenon. Although it is believed that the mode transition is strongly related to the mechanical properties, the nature of the mode transition had not been revealed. In this study, dynamic crack propagation on an elastomer was investigated using the finite element method (FEM) with a hyperviscoelastic material model. A series of pure shear test was carried out numerically with FEM simulations and crack velocities were measured under various values of tensile strain. As a result, our FEM simulations successfully reproduced the mode transition. The success of realising the mode transition phenomenon by a simple FEM model, which was achieved for the first time ever, helped to explain that the phenomenon occurs owing to a characteristic non-monotonic temporal development of principal stress near the crack tip.

Implications of tidally-varying bed stress and intermittent estuarine stratification on fine-sediment dynamics through the Mekong's tidal river to estuarine reach

NASA Astrophysics Data System (ADS)

McLachlan, R. L.; Ogston, A. S.; Allison, M. A.

2017-09-01

River gauging stations are often located upriver of tidal propagation where sediment transport processes and storage are impacted by widely varying ratios of marine to freshwater influence. These impacts are not yet thoroughly understood. Therefore, sediment fluxes measured at these stations may not be suitable for predicting changes to coastal morphology. To characterize sediment transport dynamics in this understudied zone, flow velocity, salinity, and suspended-sediment properties (concentration, size, and settling velocity) were measured within the tidal Sông Hậu distributary of the lower Mekong River, Vietnam. Fine-sediment aggregation, settling, and trapping rates were promoted by seasonal and tidal fluctuations in near-bed shear stress as well as the intermittent presence of a salt wedge and estuary turbidity maximum. Beginning in the tidal river, fine-grained particles were aggregated in freshwater. Then, in the interface zone between the tidal river and estuary, impeded near-bed shear stress and particle flux convergence promoted settling and trapping. Finally, in the estuary, sediment retention was further encouraged by stratification and estuarine circulation which protected the bed against particle resuspension and enhanced particle aggregation. These patterns promote mud export ( 1.7 t s-1) from the entire study area in the high-discharge season when fluvial processes dominate and mud import ( 0.25 t s-1) into the estuary and interface zone in the low-discharge season when estuarine processes dominate. Within the lower region of the distributaries, morphological change in the form of channel abandonment was found to be promoted within minor distributaries by feedbacks between channel depth, vertical mixing, and aggregate trapping. In effect, this field study sheds light on the sediment trapping capabilities of the tidal river - estuary interface zone, a relatively understudied region upstream of where traditional concepts place sites of deposition, and predicts how fine-sediment dynamics and morphology of large tropical deltas such as the Mekong will respond to changing fluvial and marine influences in the future.

Broadband Seismic Studies at the Mallik Gas Hydrate Research Well

NASA Astrophysics Data System (ADS)

Sun, L. F.; Huang, J.; Lyons-Thomas, P.; Qian, W.; Milkereit, B.; Schmitt, D. R.

2005-12-01

The JAPEX/JNOC/GSC et al. Mallik 3L-38, 4L-38 and 5L-38 scientific wells were drilled in the MacKenzie Delta, NWT, Canada in early 2002 primarily for carrying out initial tests of the feasibility of producing methane gas from the large gas hydrate deposits there [1]. As part of this study, high resolution seismic profiles, a pseudo-3D single fold seismic volume and broadband (8~180Hz) multi-offset vertical seismic profiles (VSP) were acquired at the Mallik site. Here, we provide details on the acquisition program, present the results of the 2D field profile, and discuss the potential implications of these observations for the structure of the permafrost and gas hydrate zones. These zones have long been problematic in seismic imaging due to the lateral heterogeneities. Conventional seismic data processing usually assume a stratified, weak-contrast elastic earth model. However, in permafrost and gas hydrate zones this approximation often becomes invalid. This leads to seismic wave scattering caused by multi-scale perturbation of elastic properties. A 3D viscoelastic finite difference modeling algorithm was employed to simulate wave propagation in a medium with strong contrast. Parameters in this modeling analysis are based on the borehole geophysical log data. In addition, an uncorrelated Vibroseis VSP data set was studied to investigate frequency-dependent absorption and velocity dispersion. Our results indicate that scattering and velocity dispersion are important for a better understanding of attenuation mechanisms in heterogeneous permafrost and gas hydrate zones. [1] Dallimore, S.R., Collett, T.S., Uchida, T., and Weber, M., 2005, Overview of the science program for the Mallik 2002 Gas Hydrate Production Research Well Program; in Scientific Results from Mallik 2002 Gas Hydrate production Research Well Program, MacKenzie Delta, Northwest Territories, Canada, (ed.) S.R. Dallimore and T.S. Collett; Geological Survey of Canada, Bulletin 585, in press.

Seismic Tomography of the Arabian-Eurasian Collision Zone and Surrounding Areas

DTIC Science & Technology

2010-05-20

zone. The crustal models correlate well with geologic and tectonic features. The upper mantle tomograms show the images of the subducted Neotethys...We first obtain Pn and Sn velocities using local and regional arrival time data. Second, we obtain the 3-D crustal P and S velocity models...teleseismic tomography provides a high-resolution, 3-D P-wave velocity model for the crust, upper mantle, and the transition zone. The crustal models

Laser ultrasonic investigations of vertical Bridgman crystal growth

NASA Astrophysics Data System (ADS)

Queheillalt, Douglas Ted

The many difficulties associated with the growth of premium quality CdTe and (Cd,Zn)Te alloys has stimulated an interest in the development of a non-invasive ultrasonic approach to monitor critical growth parameters such as the solid-liquid interface position and shape during vertical Bridgman growth. This sensor methodology is based upon the recognition that in most materials, the ultrasonic velocity (and the elastic stiffness constants that control it) of the solid and liquid phases are temperature dependent and an abrupt increase of the longitudinal wave velocity occurs upon solidification. The laser ultrasonic approach has also been used to measure the ultrasonic velocity of solid and liquid Cd0.96Zn0.04Te as a function of temperature up to 1140°C. Using longitudinal and shear wave velocity values together with data for the temperature dependent density allowed a complete evaluation of the temperature dependent single crystal elastic stiffness constants for solid and the adiabatic bulk modulus for liquid Cd0.96Zn0.04 Te. It was found that the ultrasonic velocities exhibited a strong monotonically decreasing function of temperature in the solid and liquid phases and the longitudinal wave indicated an abrupt almost 50% decrease upon melting. Because ray propagation in partially solidified bodies is complex and defines the sensing methodology, a ray tracing algorithm has been developed to analyze two-dimensional wave propagation in the diametral plane of cylindrical solid-liquid interfaces. Ray path, wavefront and time-of-flight (TOF) projections for rays that travel from a source to an arbitrarily positioned receiver on the diametral plane have been calculated and compared to experimentally measured data on a model liquid-solid interface. The simulations and the experimental results reveal that the interfacial region can be identified from transmission TOF data and when used in conjunction with a nonlinear least squares reconstruction algorithm, the interface geometry (i.e. axial location and shape) can be precisely recovered and the ultrasonic velocities of both solid and liquid phases obtained. To gain insight into the melting and solidification process, a single zone VB growth furnace was integrated with the laser ultrasonic sensor system and used to monitor the melting-solidification and directional solidification characteristics of Cd0.96Zn 0.04Te.

Supercritical fluid in the mantle transition zone deduced from H-D interdiffusion of wadsleyite

NASA Astrophysics Data System (ADS)

Sun, Wei; Yoshino, Takashi; Sakamoto, Naoya; Yurimoto, Hisayoshi

2018-02-01

Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H-D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.

Numerical simulation of two-phase flow for sediment transport in the inner-surf and swash zones

NASA Astrophysics Data System (ADS)

Bakhtyar, R.; Barry, D. A.; Yeganeh-Bakhtiary, A.; Li, L.; Parlange, J.-Y.; Sander, G. C.

2010-03-01

A two-dimensional two-phase flow framework for fluid-sediment flow simulation in the surf and swash zones was described. Propagation, breaking, uprush and backwash of waves on sloping beaches were studied numerically with an emphasis on fluid hydrodynamics and sediment transport characteristics. The model includes interactive fluid-solid forces and intergranular stresses in the moving sediment layer. In the Euler-Euler approach adopted, two phases were defined using the Navier-Stokes equations with interphase coupling for momentum conservation. The k-ɛ closure model and volume of fluid approach were used to describe the turbulence and tracking of the free surface, respectively. Numerical simulations explored incident wave conditions, specifically spilling and plunging breakers, on both dissipative and intermediate beaches. It was found that the spatial variation of sediment concentration in the swash zone is asymmetric, while the temporal behavior is characterized by maximum sediment concentrations at the start and end of the swash cycle. The numerical results also indicated that the maximum turbulent kinetic energy and sediment flux occurs near the wave-breaking point. These predictions are in general agreement with previous observations, while the model describes the fluid and sediment phase characteristics in much more detail than existing measurements. With direct quantifications of velocity, turbulent kinetic energy, sediment concentration and flux, the model provides a useful approach to improve mechanistic understanding of hydrodynamic and sediment transport in the nearshore zone.

Seismic structure of the central US crust and upper mantle: Uniqueness of the Reelfoot Rift

USGS Publications Warehouse

Pollitz, Fred; Mooney, Walter D.

2014-01-01

Using seismic surface waves recorded with Earthscope's Transportable Array, we apply surface wave imaging to determine 3D seismic velocity in the crust and uppermost mantle. Our images span several Proterozoic and early Cambrian rift zones (Mid-Continent Rift, Rough Creek Graben—Rome trough, Birmingham trough, Southern Oklahoma Aulacogen, and Reelfoot Rift). While ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences, the Reelfoot Rift is unique in its association with low mantle seismic velocity. Its mantle low-velocity zone (LVZ) is exceptionally pronounced and extends down to at least 200 km depth. This LVZ is of variable width, being relatively narrow (∼50km">∼50km wide) within the northern Reelfoot Rift, which hosts the New Madrid Seismic Zone (NMSZ). We hypothesize that this mantle volume is weaker than its surroundings and that the Reelfoot Rift consequently has relatively low elastic plate thickness, which would tend to concentrate tectonic stress within this zone. No other intraplate ancient rift zone is known to be associated with such a deep mantle low-velocity anomaly, which suggests that the NMSZ is more susceptible to external stress perturbations than other ancient rift zones.

Biogas Laminar Burning Velocity and Flammability Characteristics in Spark Ignited Premix Combustion

NASA Astrophysics Data System (ADS)

Anggono, Willyanto; Wardana, I. N. G.; Lawes, M.; Hughes, K. J.; Wahyudi, Slamet; Hamidi, Nurkholis; Hayakawa, Akihiro

2013-04-01

Spherically expanding flames propagating at constant pressure were employed to determine the laminar burning velocity and flammability characteristics of biogas-air mixtures in premixed combustion to uncover the fundamental flame propagation characteristics of a new alternative and renewable fuel. The results are compared with those from a methane-air flame. Biogas is a sustainable and renewable fuel that is produced in digestion facilities. The composition of biogas discussed in this paper consists of 66.4% methane, 30.6% carbon dioxide and 3% nitrogen. Burning velocity was measured at various equivalence ratios (phi) using a photographic technique in a high pressure fan-stirred bomb, the initial condition being at room temperature and atmospheric pressure. The flame for methane-air mixtures propagates from phi=0.6 till phi=1.3. The flame at phi >= 1.4 does not propagate because the combustion reaction is quenched by the larger mass of fuel. At phi<=0.5, it does not propagate as well since the heat of reaction is insufficient to burn the mixtures. The flame for biogas-air mixtures propagates in a narrower range, that is from phi=0.6 to phi=1.2. Different from the methane flame, the biogas flame does not propagate at phi>=1.3 because the heat absorbed by inhibitors strengthens the quenching effect by the larger mass of fuel. As in the methane flame, the biogas flame at phi<=0.5 does not propagate. This shows that the effect of inhibitors in extremely lean mixtures is small. Compared to a methane-air mixture, the flammability characteristic (flammable region) of biogas becomes narrower in the presence of inhibitors (carbon dioxide and nitrogen) and the presence of inhibitors causes a reduction in the laminar burning velocity. The inhibitor gases work more effectively at rich mixtures because the rich biogas-air mixtures have a higher fraction of carbon dioxide and nitrogen components compared to the lean biogas-air mixtures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Özer, Çağlar, E-mail: caglar.ozer@deu.edu.tr; Dokuz Eylul University, The Graduate School of Natural and Applied Sciences, Department of Geophysical Engineering, Izmir; Polat, Orhan, E-mail: orhan.polat@deu.edu.tr

In this study; we investigated velocity structure of Izmir and surroundings. We used local earthquake data which was recorded by different type of instruments and obtained high resolution 3D sections. We selected more than 400 earthquakes which were occurred between 2010 and 2013. Examined tomographic sections especially in Izmir along coastal areas (Mavisehir-Inciraltı); revealed the low speed zone. Along this low-speed zone; it is consistent with the results obtained from the stratigraphic section and surface geology. While; low velocity zones are associated with faults and water content; high velocity is related to magmatic rocks or compact rocks. Along Karsıyaka, Seferihisar,more » Orhanlı, Izmir fault zones; low P velocity was observed. When examined higher elevations of the topography; which are composed of soured magmatic material is dominated by high P velocity. In all horizontal sections; resolution decreasing with increasing depth. The reason for this; the reduction of earthquakes causes ray tracing problems.« less

Frictional, Hydraulic, and Acoustic Properties of Alpine Fault DFDP-1 Core

NASA Astrophysics Data System (ADS)

Carpenter, B. M.; Ikari, M.; Kitajima, H.; Kopf, A.; Marone, C.; Saffer, D. M.

2012-12-01

The Alpine Fault, a transpressional plate-boundary fault transecting the South Island of New Zealand, is the current focus of the Deep Fault Drilling Project (DFDP), a major fault zone drilling initiative. Phase 1 of this project included 2 boreholes that penetrated the active fault at depths of ˜100 m and ˜150 m, and provided a suite of core samples crossing the fault. Here, we report on laboratory measurements of frictional strength and constitutive behavior, permeability, and ultrasonic velocities for a suite of the recovered core samples We conducted friction experiments on powdered samples in a double-direct shear configuration at room temperature and humidity. Our results show that over a range of effective normal stresses from 10-100 MPa, friction coefficients are ~0.60-0.70, and are similar for all of the materials we tested. Rate-stepping tests document velocity-weakening behavior in the majority of wall rock samples, whereas the principal slip surface (PSS) and an adjacent clay-rich cataclasite exhibit velocity-strengthening behavior. We observe significant rates of frictional healing in all of our samples, indicating that that the fault easily regains its strength during interseismic periods. Our results indicate that seismic slip is not likely to nucleate in the clay-rich PSS at shallow depths, but might nucleate and propagate on the gouge/wall rock interface. We measured permeability using a constant head technique, on vertically oriented cylindrical mini-cores (i.e. ˜45 degrees to the plane of the Alpine Fault). We conducted these tests in a triaxial configuration, under isotropic stress conditions and effective confining pressures from ~2.5 - 63.5 MPa. We conducted ultrasonic wavespeed measurements concurrently with the permeability measurements to determine P- and S-wave velocities from time-of-flight. The permeability of all samples decreases systematically with increasing effective stress. The clay-rich cataclasite (1.37 x 10-19 m2) and PSS (1.62 x 10-20 m2) samples exhibit the lowest permeabilities. The cataclasite, and wall rock mylonite and gravel samples, all exhibit permeabilities > 10-18 m2. We also observe that permeability of the cataclasites appears to decrease with proximity to the active fault zone. Our laboratory measurements are consistent with borehole slug tests that show the fault is a hydraulic barrier, and suggest that fault rock permeability is sufficiently low to facilitate transient pore pressure effects during rapid slip, including thermal pressurization and dilatancy hardening. Elastic wave velocity increases systematically with increasing effective stress. We find the lowest P-wave velocities in clay-rich, poorly lithified samples from within and near the active fault, including hanging wall cataclasite, fault gouge, and footwall gravel. Our results are consistent with borehole logging data that show an increase in P-wave velocity from the mylonite into the competent cataclasites, and a decrease in P-wave velocity through the clay-rich cataclasite and into the fault zone.

Effect of Sediments on Rupture Dynamics of Shallow Subduction Zone Earthquakes and Tsunami Generation

NASA Astrophysics Data System (ADS)

Ma, S.

2011-12-01

Low-velocity fault zones have long been recognized for crustal earthquakes by using fault-zone trapped waves and geodetic observations on land. However, the most pronounced low-velocity fault zones are probably in the subduction zones where sediments on the seafloor are being continuously subducted. In this study I focus on shallow subduction zone earthquakes; these earthquakes pose a serious threat to human society in their ability in generating large tsunamis. Numerous observations indicate that these earthquakes have unusually long rupture durations, low rupture velocities, and/or small stress drops near the trench. However, the underlying physics is unclear. I will use dynamic rupture simulations with a finite-element method to investigate the dynamic stress evolution on faults induced by both sediments and free surface, and its relations with rupture velocity and slip. I will also explore the effect of off-fault yielding of sediments on the rupture characteristics and seafloor deformation. As shown in Ma and Beroza (2008), the more compliant hanging wall combined with free surface greatly increases the strength drop and slip near the trench. Sediments in the subduction zone likely have a significant role in the rupture dynamics of shallow subduction zone earthquakes and tsunami generation.

Along-strike complex geometry of subduction zones - an experimental approach

NASA Astrophysics Data System (ADS)

Midtkandal, I.; Gabrielsen, R. H.; Brun, J.-P.; Huismans, R.

2012-04-01

Recent knowledge of the great geometric and dynamic complexity insubduction zones, combined with new capacity for analogue mechanical and numerical modeling has sparked a number of studies on subduction processes. Not unexpectedly, such models reveal a complex relation between physical conditions during subduction initiation, strength profile of the subducting plate, the thermo-dynamic conditions and the subduction zones geometries. One rare geometrical complexity of subduction that remains particularly controversial, is the potential for polarity shift in subduction systems. The present experiments were therefore performed to explore the influence of the architecture, strength and strain velocity on complexities in subduction zones, focusing on along-strike variation of the collision zone. Of particular concern were the consequences for the geometry and kinematics of the transition zones between segments of contrasting subduction direction. Although the model design to some extent was inspired by the configuration along the Iberian - Eurasian suture zone, the results are also of significance for other orogens with complex along-strike geometries. The experiments were set up to explore the initial state of subduction only, and were accordingly terminated before slab subduction occurred. The model wasbuilt from layers of silicone putty and sand, tailored to simulate the assumed lithospheric geometries and strength-viscosity profiles along the plate boundary zone prior to contraction, and comprises two 'continental' plates separated by a thinner 'oceanic' plate that represents the narrow seaway. The experiment floats on a substrate of sodiumpolytungstate, representing mantle. 24 experimental runs were performed, varying the thickness (and thus strength) of the upper mantle lithosphere, as well as the strain rate. Keeping all other parameters identical for each experiment, the models were shortened by a computer-controlled jackscrew while time-lapse images were recorded. After completion, the models were saturated with water and frozen, allowing for sectioning and profile inspection. The experiments were invariably characterized by different along-strike patterns of deformation, so that three distinct structural domains could be distinguished in all cases. Model descriptions are subdivided accordingly, including domain CC, simulating a continent-continent collision, domain OC, characterized by continent-ocean-continent collision and domain T, representing the transition zone between domain CC and domain OC. The latter zone varied in width and complexity depending on the contrast in structural style developed in the two other domains; in cases where domain OC developed very differently from domain CC, the transition zone was generally wider and more complex. A typical experiment displayed the following features and strain history: In domain CC two principal thrust sheets are displayed, which obviously developed in an in-sequence foreland-directed fashion. The lowermost detachment nucleated at the base of the High Strength Lithospheric Mantle analogue, whereas the uppermost thrust was anchored within the "lower crust". The two thrusts operated in concert, the surface trace of the deepest dominating in the west, and the shallowest in the east. The kinematic development of domain CC could be subdivided into four stages, including initiation of a symmetrical anticline with a minute amplitude and situated directly above the velocity discontinuity defined by the plate contact (stage 1), contemporaneous development of the two thrusts (stage 2) and an associated asymmetrical anticline (stage 3) with a central collapse graben in the latest phase (stage 4). It is noted that the segment CC as seen in a clear majority of the experiments followed this pattern of development. In contrast, the configuration of domain OC displayed greater variation, and included north and south-directed subduction, folding, growth of pop-up-structures and triangle zones. In the "ocean crust" domain, stage 1 was characterized by the growth of a fault-propagation anticline with an E-W-oriented fold axis, ending with the surfacing of a north-vergent thrust. In stage 2, the contraction was concentrated to the south in the oceanic domain, again ending with the surfacing of a thrust, here with top-south transport. By continued movement (stage 3), the thrust fault propagated towards the east, crossing into the "continental" domain and linking with the fault systems of the segment CC. The structure of domain T is dominated by the interference of faults propagating westwards from the domain CC and eastwards from the domain OC, respectively. The zone of overlap in the experiment was significant, and its central part had the geometry of a double "crocodile structure" (sensuMeissner 1989), separating the two areas of northerly and southerly subduction. Hence, its development is less easily subdivided into stages. Reference: Meissner,R., 1989: Rupture, creep lamellae and crocodiles: happenings in the continental crust. Terra Nova, 1, 17-28.

Experimental study on propagation of fault slip along a simulated rock fault

NASA Astrophysics Data System (ADS)

Mizoguchi, K.

2015-12-01

Around pre-existing geological faults in the crust, we have often observed off-fault damage zone where there are many fractures with various scales, from ~ mm to ~ m and their density typically increases with proximity to the fault. One of the fracture formation processes is considered to be dynamic shear rupture propagation on the faults, which leads to the occurrence of earthquakes. Here, I have conducted experiments on propagation of fault slip along a pre-cut rock surface to investigate the damaging behavior of rocks with slip propagation. For the experiments, I used a pair of metagabbro blocks from Tamil Nadu, India, of which the contacting surface simulates a fault of 35 cm in length and 1cm width. The experiments were done with the similar uniaxial loading configuration to Rosakis et al. (2007). Axial load σ is applied to the fault plane with an angle 60° to the loading direction. When σ is 5kN, normal and shear stresses on the fault are 1.25MPa and 0.72MPa, respectively. Timing and direction of slip propagation on the fault during the experiments were monitored with several strain gauges arrayed at an interval along the fault. The gauge data were digitally recorded with a 1MHz sampling rate and 16bit resolution. When σ is 4.8kN is applied, we observed some fault slip events where a slip nucleates spontaneously in a subsection of the fault and propagates to the whole fault. However, the propagation speed is about 1.2km/s, much lower than the S-wave velocity of the rock. This indicates that the slip events were not earthquake-like dynamic rupture ones. More efforts are needed to reproduce earthquake-like slip events in the experiments. This work is supported by the JSPS KAKENHI (26870912).

Scaling properties of conduction velocity in heterogeneous excitable media

NASA Astrophysics Data System (ADS)

Shajahan, T. K.; Borek, Bartłomiej; Shrier, Alvin; Glass, Leon

2011-10-01

Waves of excitation through excitable media, such as cardiac tissue, can propagate as plane waves or break up to form reentrant spiral waves. In diseased hearts reentrant waves can be associated with fatal cardiac arrhythmias. In this paper we investigate the conditions that lead to wave break, reentry, and propagation failure in mathematical models of heterogeneous excitable media. Two types of heterogeneities are considered: sinks are regions in space in which the voltage is fixed at its rest value, and breaks are nonconducting regions with no-flux boundary conditions. We find that randomly distributed heterogeneities in the medium have a decremental effect on the velocity, and above a critical density of such heterogeneities the conduction fails. Using numerical and analytical methods we derive the general relationship among the conduction velocity, density of heterogeneities, diffusion coefficient, and the rise time of the excitation in both two and three dimensions. This work helps us understand the factors leading to reduced propagation velocity and the formation of spiral waves in heterogeneous excitable media.

Nonlinear dynamics of shells conveying pulsatile flow with pulse-wave propagation. Theory and numerical results for a single harmonic pulsation

NASA Astrophysics Data System (ADS)

Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

2017-05-01

In deformable shells conveying pulsatile flow, oscillatory pressure changes cause local movements of the fluid and deformation of the shell wall, which propagate downstream in the form of a wave. In biomechanics, it is the propagation of the pulse that determines the pressure gradient during the flow at every location of the arterial tree. In this study, a woven Dacron aortic prosthesis is modelled as an orthotropic circular cylindrical shell described by means of the Novozhilov nonlinear shell theory. Flexible boundary conditions are considered to simulate connection with the remaining tissue. Nonlinear vibrations of the shell conveying pulsatile flow and subjected to pulsatile pressure are investigated taking into account the effects of the pulse-wave propagation. For the first time in literature, coupled fluid-structure Lagrange equations of motion for a non-material volume with wave propagation in case of pulsatile flow are developed. The fluid is modeled as a Newtonian inviscid pulsatile flow and it is formulated using a hybrid model based on the linear potential flow theory and considering the unsteady viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. Contributions of pressure and velocity propagation are also considered in the pressure drop along the shell and in the pulsatile frictional traction on the internal wall in the axial direction. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior of a pressurized Dacron aortic graft conveying blood flow. A pulsatile time-dependent blood flow model is considered by applying the first harmonic of the physiological waveforms of velocity and pressure during the heart beating period. Geometrically nonlinear vibration response to pulsatile flow and transmural pulsatile pressure, considering the propagation of pressure and velocity changes inside the shell, is here presented via frequency-response curves, time histories, bifurcation diagrams and Poincaré maps. It is shown that traveling waves of pressure and velocity cause a delay in the radial displacement of the shell at different values of the axial coordinate. The effect of different pulse wave velocities is also studied. Comparisons with the corresponding ideal case without wave propagation (i.e. with the same pulsatile velocity and pressure at any point of the shell) are here discussed. Bifurcation diagrams of Poincaré maps obtained from direct time integration have been used to study the system in the spectral neighborhood of the fundamental natural frequency. By increasing the forcing frequency, the response undergoes very complex nonlinear dynamics (chaos, amplitude modulation and period-doubling bifurcation), here deeply investigated.

Method and apparatus for measuring stress

DOEpatents

Thompson, R.B.

1983-07-28

A method and apparatus for determining stress in a material independent of micro-structural variations and anisotropies. The method comprises comparing the velocities of two horizontally polarized and horizontally propagating ultrasonic shear waves with interchanged directions of propagation and polarization. The apparatus for carrying out the method comprises periodic permanent magnet-electromagnetic acoustic transducers for generating and detecting the shear waves and means for determining the wave velocities.

Method and apparatus for measuring stress

DOEpatents

Thompson, R. Bruce

1985-06-11

A method and apparatus for determining stress in a material independent of micro-structural variations and anisotropies. The method comprises comparing the velocities of two horizontally polarized and horizontally propagating ultrasonic shear waves with interchanged directions of propagation and polarization. The apparatus for carrying out the method comprises periodic permanent magnet-electromagnetic acoustic transducers for generating and detecting the shear waves and means for determining the wave velocities.

Study of dispersive and nonlinear effects of coastal wave dynamics with a fully nonlinear potential flow model

NASA Astrophysics Data System (ADS)

Benoit, Michel; Yates, Marissa L.; Raoult, Cécile

2017-04-01

Efficient and accurate numerical models simulating wave propagation are required for a variety of engineering projects including the evaluation of coastal risks, the design of protective coastal structures, and the estimation of the potential for marine renewable energy devices. Nonlinear and dispersive effects are particularly significant in the coastal zone where waves interact with the bottom, the shoreline, and coastal structures. The main challenge in developing a numerical models is finding a compromise between computational efficiency and the required accuracy of the simulated wave field. Here, a potential approach is selected and the (fully nonlinear) water wave problem is formulated using the Euler-Zakharov equations (Zakharov, 1968) describing the temporal evolution of the free surface elevation and velocity potential. The proposed model (Yates and Benoit, 2015) uses a spectral approach in the vertical (i.e. the vertical variation of the potential is approximated by a linear combination of the first NT+1 Chebyshev polynomials, following the work of Tian and Sato (2008)). The Zakharov equations are integrated in time using a fourth-order Runge-Kutta scheme with a constant time step. At each sub-timestep, the Laplace Boundary Value Problem (BVP) is solved to estimate the free surface vertical velocity using the spectral approach, with typical values of NT between 5 to 8 for practical applications. The 1DH version of the code is validated with comparisons to the experimental data set of Becq-Girard et al. (1999), which studied the propagation of irregular waves over a beach profile with a submerged bar. The nonlinear and dispersive capacities of the model are verified with the correct representation of wave-wave interactions, in particular the transfer of energy between different harmonic components during wave propagation (analysis of the transformation of the variance spectrum along the channel). Evolution of wave skewness, asymmetry and kurtosis along the bathymetric profile also compare well with the measured values. The statistical distributions of the free surface elevation and wave height, calculated from the simulated time series, are compared to those of the measurements, with particular attention paid to the extreme waves. To use this model for realistic cases with complex bathymetric variations and multidirectional wave fields, the model has been extended to two horizontal dimensions (2DH). The spectral approach in the vertical dimension is retained, while the horizontal plane is discretized with scattered nodes to maintain the model's flexibility. The horizontal derivatives are estimated with finite-difference type formulas using Radial Basis Functions (Wright and Fornberg, 2006). The 2DH version of the code is applied to simulate the propagation of regular waves over a semi-circular step, which acts as a focusing lens. The simulation results are compared to the experimental data set of Whalin (1971). The evolution of the higher harmonic amplitudes in the shallow-water zone demonstrates the ability of the model to simulate wave propagation over complex 2DH coastal bathymetries. References: Becq-Girard F., Forget P., Benoit M. (1999) Non-linear propagation of unidirectional wave fields over varying topography. Coastal Eng., 38, 91-113. Tian Y., Sato S. (2008) A numerical model on the interaction between nearshore nonlinear waves and strong currents. Coast. Eng. Journal, 50(4), 369-395. Whalin R.W. (1971) The limit of applicability of linear wave refraction theory in a convergence zone. Technical report, DTIC Documents. Wright G.B., Fornberg B. (2006) Scattered node compact finite difference-type formulas generated from radial basis functions. J. Comp. Phys., 212, 99-123. Yates M.L., Benoit M. (2015) Accuracy and efficiency of two numerical methods of solving the potential flow problem for highly nonlinear and dispersive water waves. Int. J. Numer. Meth. Fluids, 77, 616-640. Zakharov V.E. (1968) Stability of periodic waves of finite amplitude on the surface of a deep fluid. J. Appl. Mech. Tech. Phys., 9(2), 190-194.

Beam propagation modeling of modified volume Fresnel zone plates fabricated by femtosecond laser direct writing.

PubMed

Srisungsitthisunti, Pornsak; Ersoy, Okan K; Xu, Xianfan

2009-01-01

Light diffraction by volume Fresnel zone plates (VFZPs) is simulated by the Hankel transform beam propagation method (Hankel BPM). The method utilizes circularly symmetric geometry and small step propagation to calculate the diffracted wave fields by VFZP layers. It is shown that fast and accurate diffraction results can be obtained with the Hankel BPM. The results show an excellent agreement with the scalar diffraction theory and the experimental results. The numerical method allows more comprehensive studies of the VFZP parameters to achieve higher diffraction efficiency.

Matter-wave propagation in optical lattices: geometrical and flat-band effects

DOE PAGES

Metcalf, Mekena; Chern, Gia-Wei; Di Ventra, Massimiliano; ...

2016-03-17

Here we report that the geometry of optical lattices can be engineered allowing the study of atomic transport along paths arranged in patterns that are otherwise difficult to probe in the solid state. A question feasible to atomic systems is related to the speed of propagation of matter-waves as a function of the lattice geometry. To address this issue, we have investigated theoretically the quantum transport of non-interacting and weakly-interacting ultracold fermionic atoms in several 2D optical lattice geometries. We find that the triangular lattice has a higher propagation velocity compared to the square lattice, and the cross-linked square latticemore » has an even faster propagation velocity. The increase results from the mixing of the momentum states which leads to different group velocities in quantum systems. Standard band theory provides an explanation and allows for a systematic way to search and design systems with controllable matter-wave propagation. Moreover, the presence of a flat band such as in a two-leg ladder geometry leads to a dynamical density discontinuity due to its localized atoms. Lastly, we discuss possible realizations of those dynamical phenomena.« less

Improving Thermal Ablation Delineation With Electrode Vibration Elastography Using a Bidirectional Wave Propagation Assumption

PubMed Central

DeWall, Ryan J.; Varghese, Tomy

2013-01-01

Thermal ablation procedures are commonly used to treat hepatic cancers and accurate ablation representation on shear wave velocity images is crucial to ensure complete treatment of the malignant target. Electrode vibration elastography is a shear wave imaging technique recently developed to monitor thermal ablation extent during treatment procedures. Previous work has shown good lateral boundary delineation of ablated volumes, but axial delineation was more ambiguous, which may have resulted from the assumption of lateral shear wave propagation. In this work, we assume both lateral and axial wave propagation and compare wave velocity images to those assuming only lateral shear wave propagation in finite element simulations, tissue-mimicking phantoms, and bovine liver tissue. Our results show that assuming bidirectional wave propagation minimizes artifacts above and below ablated volumes, yielding a more accurate representation of the ablated region on shear wave velocity images. Area overestimation was reduced from 13.4% to 3.6% in a stiff-inclusion tissue-mimicking phantom and from 9.1% to 0.8% in a radio-frequency ablation in bovine liver tissue. More accurate ablation representation during ablation procedures increases the likelihood of complete treatment of the malignant target, decreasing tumor recurrence. PMID:22293748

Improving thermal ablation delineation with electrode vibration elastography using a bidirectional wave propagation assumption.

PubMed

DeWall, Ryan J; Varghese, Tomy

2012-01-01

Thermal ablation procedures are commonly used to treat hepatic cancers and accurate ablation representation on shear wave velocity images is crucial to ensure complete treatment of the malignant target. Electrode vibration elastography is a shear wave imaging technique recently developed to monitor thermal ablation extent during treatment procedures. Previous work has shown good lateral boundary delineation of ablated volumes, but axial delineation was more ambiguous, which may have resulted from the assumption of lateral shear wave propagation. In this work, we assume both lateral and axial wave propagation and compare wave velocity images to those assuming only lateral shear wave propagation in finite element simulations, tissue-mimicking phantoms, and bovine liver tissue. Our results show that assuming bidirectional wave propagation minimizes artifacts above and below ablated volumes, yielding a more accurate representation of the ablated region on shear wave velocity images. Area overestimation was reduced from 13.4% to 3.6% in a stiff-inclusion tissue-mimicking phantom and from 9.1% to 0.8% in a radio-frequency ablation in bovine liver tissue. More accurate ablation representation during ablation procedures increases the likelihood of complete treatment of the malignant target, decreasing tumor recurrence. © 2012 IEEE

Using the Vertical Component of the Surface Velocity Field to Map the Locked Zone at Cascadia Subduction Zone

NASA Astrophysics Data System (ADS)

Moulas, E.; Brandon, M. T.; Podladchikov, Y.; Bennett, R. A.

2014-12-01

At present, our understanding of the locked zone at Cascadia subduction zone is based on thermal modeling and elastic modeling of horizontal GPS velocities. The thermal model by Hyndman and Wang (1995) provided a first-order assessment of where the subduction thrust might be cold enough for stick-slip behavior. The alternative approach by McCaffrey et al. (2007) is to use a Green's function that relates horizontal surface velocities, as recorded by GPS, to interseismic elastic deformation. The thermal modeling approach is limited by a lack of information about the amount of frictional heating occurring on the thrust (Molnar and England, 1990). The GPS approach is limited in that the horizontal velocity component is fairly insensitive to the structure of the locked zone. The vertical velocity component is much more useful for this purpose. We are fortunate in that vertical velocities can now be measured by GPS to a precision of about 0.2 mm/a. The dislocation model predicts that vertical velocities should range up to about 20 percent of the subduction velocity, which means maximum values of ~7 mm/a. The locked zone is generally entirely offshore at Cascadia, except for the Olympic Peninsula region, where the underlying Juan De Fuca plate has an anomalously low dip. Previous thermal and GPS modeling, as well as tide gauge data and episodic tremors indicate the locked zone there extends about 50 to 75 km onland. This situation provides an opportunity to directly study the locked zone. With that objective in mind, we have constructed a full 3D geodynamic model of the Cascadia subduction zone. At present, the model provides a full representation of the interseismic elastic deformation due to variations of slip on the subduction thrust. The model has been benchmarked against the Savage (2D) and Okada (3D) analytical solutions. This model has an important advantage over traditional dislocation modeling in that we include temperature-sensitive viscosity for the upper and lower plates, and also use realistic constitutive models to represent the locked zone. Another important advantage is that the 3D model provides a full representation of the interseismic deformation, which is important for interpreting GPS data.

Group velocity of discrete-time quantum walks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kempf, A.; Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1; Portugal, R.

2009-05-15

We show that certain types of quantum walks can be modeled as waves that propagate in a medium with phase and group velocities that are explicitly calculable. Since the group and phase velocities indicate how fast wave packets can propagate causally, we propose the use of these wave velocities in our definition for the hitting time of quantum walks. Our definition of hitting time has the advantage that it requires neither the specification of a walker's initial condition nor of an arrival probability threshold. We give full details for the case of quantum walks on the Cayley graphs of Abelianmore » groups. This includes the special cases of quantum walks on the line and on hypercubes.« less

Precise seismic velocity structure beneath the Hokkaido corner, northern Japan: Arc-arc collision and the 1970 M 6.7 Hidaka region earthquake and the 1982 M 7.1 Urakawa-oki earthquake

NASA Astrophysics Data System (ADS)

Kita, S.; Hasegawa, A.; Nakajima, J.; Okada, T.; Matsuzawa, T.; Katsumata, K.

2011-12-01

Using arrival-time data both from the nationwide Kiban seismic network and from a dense temporary seismic network covering the area of the Hokkaido corner [Katsumata et al., 2002a; 2003, JGR], we precisely determined three-dimensional seismic velocity structure beneath this area to understand the collision process between the Kuril and northeasetern Japan forearcs. Tomographic inversions were performed with smaller grid spacing [5 x 10 x 5 km] than our previous study [Kita et al., 2010b, EPSL] by using the double-difference tomography method [Zhang and Thurber, 2003; 2006]. Inhomogeneous seismic velocity structure was more precisely imaged in the Hokkaido corner at depths of 0-120 km. A broad low-velocity zone of P- and S- waves having velocities of crust materials with a total volume of 80 km x 100 km x 50 km is distributed to the west of the Hidaka metamorphic belt (the Hidaka main thrust) at depths of 30-90km. On the other hand, several small-scale high-velocity zones having velocities of mantle materials were detected at depths of 0-35 km), inclined east-northeastward at a high angle of 40-60 degrees. All of these anomaly high velocity zones are respectively located in the deeper extension of the Neogene thrust faults, striking almost N-S direction and dipping 40-50 degrees at depths of 0-10km [e.g. Ito 2000]. The largest high-velocity zone is located in the deeper extension of the Hidaka main thrust, being in contact with the eastern edge of the low-V zone. This high-V zone reaches near the surface at the Hidaka metamorphic belt and its southern edge is located just beneath the Horoman-peridotite, which is one of the most famous peridotite outcrops. Moreover, the boundary of the high-V zone with the broad low-V zone corresponds to the fault plane of the 1970 Mj 6.7 Hidaka region earthquake [Moriya 1972]. Another high-V zone is located within the broad low-V zone at depths of 20-30km and in the deeper extension of thrust, which belongs to the Ishikari Low land eastern edge fault groups. The western boundary of this small high-V zone corresponds to the fault plane of the 1982 Mj 7.1 Urakawa-oki earthquake [Moriya et al, 1983]. Both of the hanging walls of the fault planes of two M 7 class big earthquakes have anomalously high velocities, while both of the foot walls have low velocities. A considerable number of earthquakes, including aftershocks of these two big earthquake and, occur in the broad low-V zone at depths of 0-80 km (even at depths of the mantle wedge), whereas seismicity is very low in other areas. These present observations provide important in formation to deepen our understanding of the ongoing arc-arc collision process and earthquake generation mechanism in the Hokkaido corner.

Earthquakes in the Orozco transform zone: seismicity, source mechanisms, and tectonics

USGS Publications Warehouse

Tréhu, Anne M.; Solomon, Sean C.

1983-01-01

As part of the Rivera Ocean Seismic Experiment, a network of ocean bottom seismometers and hydrophones was deployed in order to determine the seismic characteristics of the Orozco transform fault in the central eastern Pacific. We present hypocentral locations and source mechanisms for 70 earthquakes recorded by this network. All epicenters are within the transform region of the Orozco Fracture Zone and clearly delineate the active plate boundary. About half of the epicenters define a narrow line of activity parallel to the spreading direction and situated along a deep topographic trough that forms the northern boundary of the transform zone (region 1). Most focal depths for these events are very shallow, within 4 km of the seafloor; several well-determined focal depths, however, are as great as 7 km. No shallowing of seismic activity is observed as the rise-transform intersection is approached; to the contrary, the deepest events are within 10 km of the intersection. First motion polarities for most of the earthquakes in region 1 are compatible with right-lateral strike slip faulting along a nearly vertical plane, striking parallel to the spreading direction. Another zone of activity is observed in the central part of the transform (region 2). The apparent horizontal and vertical distribution of activity in this region is more scattered than in the first, and the first motion radiation patterns of these events do not appear to be compatible with any known fault mechanism. Pronounced lateral variations in crustal velocity structure are indicated for the transform region from refraction data and measurements of wave propagation directions. The effect of this lateral heterogeneity on hypocenters and fault plane solutions is evaluated by tracing rays through a three-dimensional velocity grid. While findings for events in region 1 are not significantly affected, in region 2, epicentral mislocations of up to 10 km and azimuthal deflections of up to 45° may result from assuming a laterally homogeneous velocity structure. When corrected for the effects of lateral heterogeneity, the epicenters and fault plane solutions for earthquakes in region 2 are compatible with predominantly normal faulting along a topographic trough trending NW–SE; the focal depths, however, are poorly constrained. These results suggest an en echelon spreading center or leaky transform regime in the central transform region.

Oppositely directed pairs of propagating rifts in back-arc basins: Double saloon door seafloor spreading during subduction rollback

NASA Astrophysics Data System (ADS)

Martin, A. K.

2006-06-01

When a continent breaks up into two plates, which then separate from each other about a rotation pole, it can be shown that if initial movement is taken up by lithospheric extension, asthenospheric breakthrough and oceanic accretion propagate toward the pole of rotation. Such a propagating rift model is then applied to an embryonic centrally located rift which evolves into two rifts propagating in opposite directions. The resultant rhombic shape of the modeled basin, initially underlain entirely by thinned continental crust, is very similar to the Oligocene to Burdigalian back-arc evolution of the Valencia Trough and the Liguro-Provencal Basin in the western Mediterranean. Existing well and seismic stratigraphic data confirm that a rift did initiate in the Gulf of Lion and propagated southwest into the Valencia Trough. Similarly, seismic refraction, gravity, and heat flow data demonstrate that maximum extension within the Valencia Trough/Liguro-Provencal Basin occurred in an axial position close to the North Balearic Fracture Zone. The same model of oppositely propagating rifts, when applied to the Burdigalian/Langhian episode of back-arc oceanic accretion within the Liguro-Provencal and Algerian basins, predicts a number of features which are borne out by existing geological and geophysical, particularly magnetic data. These include the orientation of subparallel magnetic anomalies, presumed to be seafloor spreading isochrons, in both basins; concave-to-the-west fracture zones southwest of the North Balearic Fracture Zone, and concave-to-the-east fracture zones to its northeast; a spherical triangular area of NW oriented seafloor spreading isochrons southwest of Sardinia; the greater NW extension of the central (youngest?) magnetic anomaly within this triangular area, in agreement with the model-predicted northwestward propagation of a rift in this zone; successively more central (younger) magnetic anomalies abutting thinned continental crust nearer to the pole of rotation in the Liguro-Provencal Basin. The latter feature demonstrates that a rift also propagated northeast in the Liguro-Provencal Basin, at least in its oceanic accretion phase of development. An adaptation of an existing model for subduction slab detachment occurring along the North African margin in the late Burdigalian/Langhian, proposes propagation in opposite directions of the slab tear. The resultant rhombic slab detachment is closely associated in space and time with the rhombic form of the Algerian/Liguro-Provencal basins, suggesting a cause and effect relationship.

Insights upon upper crustal arhitecture of a subduction zone and its surroundings - Vrancea Zone and Focsani Basin - substantiated by geophysical studies

NASA Astrophysics Data System (ADS)

Bocin, A.; Stephenson, R.; Mocanu, V.

2007-12-01

The DACIA PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the proposed objective of obtaining new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basin developed within and adjacent to the Vrancea zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly NW-SE direction, from near the southeast Transylvanian Basin, across the mountainous southeastern Carpathians and their foreland to near the Danube River. A high resolution 2.5D velocity model of the upper crust along the seismic profile has been determined from a tomographic inversion and a 2D ray tracing forward modelling of the DACIA PLAN first arrival data. Peculiar shallow high velocities indicate that pre-Tertiary basement in the Vrancea Zone (characterised by velocities greater than 5.6 km/s) is involved in Carpathian thrusting while rapid alternance, vertically or horizontally, of velocity together with narrowingly contemporary crustal events suggests uplifting. Further to the east, at the foreland basin-thrust belt transition zone (well defined within velocity values), the velocity model suggests a nose of the Miocene Subcarpathians nappe being underlain by Focsani Basin units. A Miocene and younger Focsani Basin sedimentary succession of ~10 km thickness is ascertained by a gradual increase of velocities and strongly defined velocity boundaries.

Solitary waves in a peridynamic elastic solid

DOE PAGES

Silling, Stewart A.

2016-06-23

The propagation of large amplitude nonlinear waves in a peridynamic solid is ana- lyzed. With an elastic material model that hardens in compression, sufficiently large wave pulses propagate as solitary waves whose velocity can far exceed the linear wave speed. In spite of their large velocity and amplitude, these waves leave the material they pass through with no net change in velocity and stress. They are nondissipative and nondispersive, and they travel unchanged over large distances. An approximate solution for solitary waves is derived that reproduces the main features of these waves observed in computational simulations. We demonstrate, by numericalmore » studies, that waves interact only weakly with each other when they collide. Finally, we found that wavetrains composed of many non-interacting solitary waves form and propagate under certain boundary and initial conditions.« less

In-situ Observations of Swash-zone Flow Velocities and Sediment Transport on a Steep Beach

NASA Astrophysics Data System (ADS)

Chardon-Maldonado, P.; Puleo, J. A.; Figlus, J.

2014-12-01

A 45 m scaffolding frame containing an array of instruments was installed at South Bethany Beach, Delaware, to obtain in-situ measurements in the swash zone. Six cross-shore stations were established to simultaneously measure near-bed velocity profiles, sediment concentration and water level fluctuations on a steep beach. Measurements of swash-zone hydrodynamics and morphological change were collected from February 12 to 25, 2014, following a large Nor'easter storm with surf zone significant wave height exceeding 5 m. Swash-zone flow velocities (u,v,w) were measured at each cross-shore location using a Nortek Vectrino profiling velocimeter that measured a 30 mm velocity profile at 1 mm vertical increments at 100 Hz. These velocity profiles were used to quantify the vertical flow structure over the foreshore and estimate hydrodynamic parameters such as bed shear stress and turbulent kinetic energy dissipation. Sediment concentrations were measured using optical backscatter sensors (OBS) to obtain spatio-temporal measurements during both uprush and backwash phases of the swash cycle. Cross-shore sediment transport rates at each station were estimated by taking the product of cross-shore velocity and sediment concentration. Foreshore elevations were sampled every low tide using a Leica GPS system with RTK capability. Cross-shore sediment transport rates and gradients derived from the velocities and bed shear stress estimates will be related to the observed morphological change.

3D P-wave velocity structure of the crust and relocation of earthquakes in the Lushan, China, source area

NASA Astrophysics Data System (ADS)

Yu, Xiangwei; Wang, Xiaona; Zhang, Wenbo

2016-04-01

Many researchers have investigated the Lushan source area with geological and geophysical approaches since the 2013 Lushan, China, earthquake happened. Compared with the previous tomographic studies, we have used a much large data set and an updated tomographic method to determine a small scale three-dimensional P wave velocity structure with spatial resolution less than 5km, which plays the important role for understanding the deep structure and the genetic mechanism beneath the Lushan area. The double difference seismic tomography method is applied to 50,711 absolute first arrival P wave arrival times and 7,294,691 high quality relative P arrival times of 5,285 events of Lushan seismic sequence to simultaneously determine the detailed crustal 3D P wave velocity structure and the hypocenter parameters in the Lushan seismic area. This method takes account of the path anomaly biases explicitly by making full use of valuable information of seismic wave propagation jointly with absolute and relative arrival time data. Our results show that the Lushan mainshock locates at 30.28N, 103.98E, with the depth of 16.38km. The front edge of aftershock in the northeast of mainshock present a spade with a steep dip angle, the aftershocks' extended length is about 12km. In the southwest of Lushan mainshock, the front edge of aftershock in low velocity zone slope gently, the aftershocks' extended length is about 23km. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. The Tianquan, Shuangshi and Daguan line lies in the transition zone between high velocity anomalies to the southeast and low velocity anomalies to the northwest at the ground surface. An obvious high-velocity anomaly is visible in Daxing area. With the depth increasing, Baoxing high velocity anomaly extends to Lingguan, while the southeast of the Tianquan, Shuangshi and Daguan line still shows low velocity. The high-velocity anomalies beneath Baoxing and Daxing connect each other in 10km depth, which makes the contrast between high and low velocity anomalies more sharp. Above 20km depth the velocity structure in southwest and northeast segment of mainshock shows a big difference: low-velocity anomalies are dominated the southwest segment, while high-velocity anomalies rule the northeast segment. Lushan aftershocks in southwest are distributed in low-velocity anomalies or the transition belt: the footwall represents low-velocity anomalies, while the hanging wall shows high-velocity anomalies. The northeastern aftershocks are distributed at the boundary between high-velocity anomalies in Baoxing and Daxing area. The P wave velocity structure of Lushan seismic area shows obviously lateral heterogeneity. The P wave velocity anomalies represent close relationship with topographic relief and geological structure. In Baoxingarea the complex rocks correspond obvious high-velocity anomalies extending down to 15km depth，while the Cenozoic rocks are correlated with low-velocity anomalies. Lushan mainshock locates at the leading edge of a low-velocity anomaly surrounded by the Baoxing and Daxing high-velocity anomalies. The main seismogenic layer dips to northwest. Meanwhile, a recoil seismic belt dips to southeast above the main seismogenic layer exists at the lower boundary of Baoxing high-velocity anomaly.

Co-ordinated spatial propagation of blood plasma clotting and fibrinolytic fronts

PubMed Central

Zhalyalov, Ansar S.; Panteleev, Mikhail A.; Gracheva, Marina A.; Ataullakhanov, Fazoil I.

2017-01-01

Fibrinolysis is a cascade of proteolytic reactions occurring in blood and soft tissues, which functions to disintegrate fibrin clots when they are no more needed. In order to elucidate its regulation in space and time, fibrinolysis was investigated using an in vitro reaction-diffusion experimental model of blood clot formation and dissolution. Clotting was activated by a surface with immobilized tissue factor in a thin layer of recalcified blood plasma supplemented with tissue plasminogen activator (TPA), urokinase plasminogen activator or streptokinase. Formation and dissolution of fibrin clot was monitored by videomicroscopy. Computer systems biology model of clot formation and lysis was developed for data analysis and experimental planning. Fibrin clot front propagated in space from tissue factor, followed by a front of clot dissolution propagating from the same source. Velocity of lysis front propagation linearly depended on the velocity clotting front propagation (correlation r2 = 0.91). Computer model revealed that fibrin formation was indeed the rate-limiting step in the fibrinolysis front propagation. The phenomenon of two fronts which switched the state of blood plasma from liquid to solid and then back to liquid did not depend on the fibrinolysis activator. Interestingly, TPA at high concentrations began to increase lysis onset time and to decrease lysis propagation velocity, presumably due to plasminogen depletion. Spatially non-uniform lysis occurred simultaneously with clot formation and detached the clot from the procoagulant surface. These patterns of spatial fibrinolysis provide insights into its regulation and might explain clinical phenomena associated with thrombolytic therapy. PMID:28686711

Observations of a cycle of intense coastal upwelling and downwelling at the research site of the Shirshov Institute of Oceanology in the Black Sea

NASA Astrophysics Data System (ADS)

Zatsepin, A. G.; Silvestrova, K. P.; Kuklev, S. B.; Piotoukh, V. B.; Podymov, O. I.

2016-03-01

The paper presents the results of joint analysis of the response of vertical temperature and current velocity profile distributions in the coastal zone of the Gelendzhik region of the Black Sea to strong wind forcing in the third ten-day period of September 2013. This forcing was caused by the propagation of an atmospheric cyclone, which first initiated coastal upwelling that was later replaced by downwelling. We formulate a criterion for the development of full coastal upwelling and demonstrate its efficiency. We assume that frequent events of incomplete coastal upwelling and downwelling are associated with changes in the water dynamics (variations in the intensity and direction of the alongshore current) generally not related to local wind forcing.

Modeling of plasticity and fracture of metals at shock loading

NASA Astrophysics Data System (ADS)

Mayer, A. E.; Khishchenko, K. V.; Levashov, P. R.; Mayer, P. N.

2013-05-01

In this paper, we present a model of dislocation plasticity and fracture of metals, which in combination with the wide-range equation of state and the continuum mechanics equations is a necessary component for simulation of the shock-wave loading. We take into account immobilization of dislocations and nucleation of micro-voids in weakened zones of substance; this is distinguished feature of the present version of the model. Accounting of the dislocations immobilization provides a better description of the unloading wave structure, while the detailed consideration of processes in the weakened zones expands the domain of applicability of fracture model to higher strain rates. We compare our results with the experimental data for the shock loading of aluminum, copper, and nickel samples; the comparison indicates satisfactory description of the elastic precursor, unloading wave, and spall pulse. Using the model, we investigate intently the early stage of the shock formation in solids; it is found out that the elastic precursor is formed even for a strong shock wave, and initially the precursor has very large amplitude and propagation velocity.

Ocean-ice interaction in the marginal ice zone using synthetic aperture radar imagery

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Peng, Chich Y.; Weingartner, Thomas J.

1994-01-01

Ocean-ice interaction processes in the marginal ice zone (MIZ) by wind, waves, and mesoscale features, such as up/downwelling and eddies are studied using Earth Remote-Sensing Satellite (ERS) 1 synthetic aperture radar (SAR) images and an ocean-ice interaction model. A sequence of seven SAR images of the MIZ in the Chukchi Sea with 3 or 6 days interval are investigated for ice edge advance/retreat. Simultaneous current measurements from the northeast Chukchi Sea, as well as the Barrow wind record, are used to interpret the MIZ dynamics. SAR spectra of waves in ice and ocean waves in the Bering and Chukchi Sea are compared for the study of wave propagation and dominant SAR imaging mechanism. By using the SAR-observed ice edge configuration and wind and wave field in the Chukchi Sea as inputs, a numerical simulation has been performed with the ocean-ice interaction model. After 3 days of wind and wave forcing the resulting ice edge configuration, eddy formation, and flow velocity field are shown to be consistent with SAR observations.

Experimental investigation of piloted flameholders

NASA Technical Reports Server (NTRS)

Guo, C. F.; Zhang, Y. H.; Xie, Q. M.

1986-01-01

Four configurations of piloted flameholders were tested. The range of flame stabilization, flame propagation, pressure oscillation during ignition, and pressure drop of the configurations were determined. Some tests showed a very strong effect of inlet flow velocity profile and flameholder geometry on flame stabilization. These tests led to the following conclusions. (1) The use of a piloted flameholder in the turbofan augmentor may minimize the peak pressure rise during ignition. At the present experimental conditions, delta P/P asterisk over 2 is less than 10 percent; therefore, the use of a piloted flameholder is a good method to realize soft ignition. (2) The geometry of the piloted flameholder and the amount of fuel injected into the flameholder have a strong effect on the pressure oscillation during ignition of the fuel-air mixture in the secondary zone. (3) Compared with the V-gutter flameholder with holes in its wall, the V-gutter flameholder without holes not only has advantages such as simple structure and good rigidity but offers a wide combustion stability limit and a high capability of igniting the fuel-air mixture of the secondary zone.

VP Structure of Mount St. Helens, Washington, USA, imaged with local earthquake tomography

USGS Publications Warehouse

Waite, G.P.; Moran, S.C.

2009-01-01

We present a new P-wave velocity model for Mount St. Helens using local earthquake data recorded by the Pacific Northwest Seismograph Stations and Cascades Volcano Observatory since the 18 May 1980 eruption. These data were augmented with records from a dense array of 19 temporary stations deployed during the second half of 2005. Because the distribution of earthquakes in the study area is concentrated beneath the volcano and within two nearly linear trends, we used a graded inversion scheme to compute a coarse-grid model that focused on the regional structure, followed by a fine-grid inversion to improve spatial resolution directly beneath the volcanic edifice. The coarse-grid model results are largely consistent with earlier geophysical studies of the area; we find high-velocity anomalies NW and NE of the edifice that correspond with igneous intrusions and a prominent low-velocity zone NNW of the edifice that corresponds with the linear zone of high seismicity known as the St. Helens Seismic Zone. This low-velocity zone may continue past Mount St. Helens to the south at depths below 5??km. Directly beneath the edifice, the fine-grid model images a low-velocity zone between about 2 and 3.5??km below sea level that may correspond to a shallow magma storage zone. And although the model resolution is poor below about 6??km, we found low velocities that correspond with the aseismic zone between about 5.5 and 8??km that has previously been modeled as the location of a large magma storage volume. ?? 2009 Elsevier B.V.

Propellant Crack Tip Ignition and Propagation under Rapid Pressurization

DTIC Science & Technology

1982-10-01

that the ignition-delay time decreases and the heat flux to the propellant surface increases as the pressurization rate is increased. The decrease in...leading to ignition. The model predicts the experimental obseriation that the ignition delay time decreases as the pressurization rate is increased...pressurization rate on both crack propagation velocity and time variation of crack shape was studied. Experimental results indicated that the crack velocity

Modelling blast induced damage from a fully coupled explosive charge

PubMed Central

Onederra, Italo A.; Furtney, Jason K.; Sellers, Ewan; Iverson, Stephen

2015-01-01

This paper presents one of the latest developments in the blasting engineering modelling field—the Hybrid Stress Blasting Model (HSBM). HSBM includes a rock breakage engine to model detonation, wave propagation, rock fragmentation, and muck pile formation. Results from two controlled blasting experiments were used to evaluate the code’s ability to predict the extent of damage. Results indicate that the code is capable of adequately predicting both the extent and shape of the damage zone associated with the influence of point-of-initiation and free-face boundary conditions. Radial fractures extending towards a free face are apparent in the modelling output and matched those mapped after the experiment. In the stage 2 validation experiment, the maximum extent of visible damage was of the order of 1.45 m for the fully coupled 38-mm emulsion charge. Peak radial velocities were predicted within a relative difference of only 1.59% at the nearest history point at 0.3 m from the explosive charge. Discrepancies were larger further away from the charge, with relative differences of −22.4% and −42.9% at distances of 0.46 m and 0.61 m, respectively, meaning that the model overestimated particle velocities at these distances. This attenuation deficiency in the modelling produced an overestimation of the damage zone at the corner of the block due to excessive stress reflections. The extent of visible damage in the immediate vicinity of the blasthole adequately matched the measurements. PMID:26412978

New Orogenic Model for Taiwan Collision Zone Inferred From Three-dimensional P- and S-wave Velocity Structures and Seismicity

NASA Astrophysics Data System (ADS)

Nagai, S.; Hirata, N.; Sato, H.

2008-12-01

The island of Taiwan is located in the site of ongoing arc-continent collision zone between the Philippine Sea Plate (PSP) and the Eurasian Plate (EUP). Numerous geophysical and geological studies are done in and around Taiwan to develop various models to explain the tectonic processes in the Taiwan region. However, their details have not been known enough, especially under the Central Range. We suggest a new orogenic model for Taiwan orogeny, named 'Upper Crustal Stacking Model', inferred from our tomographic images using three temporary seismic networks with the Central Weather Bureau Seismic Network. These three temporary networks are the aftershock observation after the 1999 Chi-Chi Taiwan earthquake and two dense array observations across central and southern Taiwan, respectively. Tomographic images by the double-difference tomography [Zhang and Thurber, 2003] show a lateral alternate variation of high- and low-velocity, which are well correlated to surface geology and separated by east-dipping boundaries. These images have reliable high-resolution by dense arrays to be able to discuss this alternate variation. We found three high-velocity zones (> 6.0km/s). The westernmost zone corresponds to the subducting EUP. Other two zones are located beneath the Hsuehshan Range and the Eastern Central Range with trends of eastward dipping, respectively. And, we could image low-velocity zone located beneath Backbone Range between the two high-velocity zones clearly. We interpret that these east-dipping high- and low-velocity zones can be divided into two layered blocks and the subducting EUP, each of which consists of a high-velocity body under low-velocity one. Layered blocks can be interpreted as stacked thrust sheets between the subducting EUP and the Northern Luzon Arc, a part of PSP. These thrust sheets are parts of upper- and mid-crust detached from the subducting EUP. The model of continental subduction followed by buoyancy-driven exhumation can explain the existence of stacked thrust sheets. Thus we propose a new orogenic model, as referred to as the 'Upper Crustal Stacking Model'.

Dynamic delamination crack propagation in a graphite/epoxy laminate

NASA Technical Reports Server (NTRS)

Grady, J. E.; Sun, C. T.

1991-01-01

Dynamic delamination crack propagation in a (90/0) 5s Graphite/Epoxy laminate with an embedded interfacial crack was investigated experimentally using high speed photography. The dynamic motion was produced by impacting the beamlike laminate specimen with a silicon rubber ball. The threshold impact velocities required to initiate dynamic crack propagation in laminates with varying initial crack positions were determined. The crack propagation speeds were estimated from the photographs. Results show that the through the thickness position of the embedded crack can significantly affect the dominant mechanism and the threshold impact velocity for the onset of crack movement. If the initial delamination is placed near the top of bottom surface of the laminate, local buckling of the delaminated plies may cause instability of the crack. If the initial delamination lies on the midplane, local buckling does not occur and the initiation of crack propagation appears to be dominated by Mode II fracture. The crack propagation and arrest observed was seen to be affected by wave motion within the delamination region.

S-velocity structure in Cimandiri fault zone derived from neighbourhood inversion of teleseismic receiver functions

NASA Astrophysics Data System (ADS)

Syuhada; Anggono, T.; Febriani, F.; Ramdhan, M.

2018-03-01

The availability information about realistic velocity earth model in the fault zone is crucial in order to quantify seismic hazard analysis, such as ground motion modelling, determination of earthquake locations and focal mechanism. In this report, we use teleseismic receiver function to invert the S-velocity model beneath a seismic station located in the Cimandiri fault zone using neighbourhood algorithm inversion method. The result suggests the crustal thickness beneath the station is about 32-38 km. Furthermore, low velocity layers with high Vp/Vs exists in the lower crust, which may indicate the presence of hot material ascending from the subducted slab.

Data-driven layer-stripping strategy in 3-D joint refraction and reflection travel-time tomography with TOMO3D

NASA Astrophysics Data System (ADS)

Meléndez, Adrià; Korenaga, Jun; Sallarès, Valentí; Miniussi, Alain; Ranero, César

2015-04-01

We present a new 3-D travel-time tomography code (TOMO3D) for the modelling of active-source seismic data that uses the arrival times of both refracted and reflected seismic phases to derive the propagation velocity distribution and the geometry of reflecting boundaries in the subsurface. The combination of refracted and reflected data provides a denser coverage of the study area. Moreover, because refractions only depend on the velocity parameters, they contribute to the mitigation of the negative effect of the ambiguity between layer thickness and propagation velocity that is intrinsic to the reflections that define these boundaries. This code is based on its renowned 2-D version TOMO2D from which it inherited the methods to solve the forward and inverse problems. The forward travel-time calculations are conducted using a hybrid ray-tracing technique combining the graph or shortest path method and the bending method. The LSQR algorithm is used to perform the iterative inversion of travel-time residuals to update the initial velocity and depth models. In order to cope with the increased computational demand due to the incorporation of the third dimension, the forward problem solver, which takes by far most of the run time (~90%), has been parallelised with a combination of MP and MPI standards. This parallelisation distributes the ray-tracing and travel-time calculations among the available computational resources, allowing the user to set the number of nodes, processors and cores to be used. The code's performance was evaluated with a complex synthetic case simulating a subduction zone. The objective is to retrieve the velocity distribution of both upper and lower plates and the geometry of the interplate and Moho boundaries. Our tomography method is designed to deal with a single reflector per inversion, and we show that a data-driven layer-stripping strategy allows to successfully recover several reflectors in successive inversions. This strategy consists in building the final velocity model layer by layer, sequentially extending it down with each inversion of a new, deeper reflector. One advantage of layer stripping is that it allows us to introduce and keep strong velocity contrasts associated to geological discontinuities that would otherwise be smoothened. Another advantage is that it poses simpler inverse problems at each step, facilitating the minimisation of travel-time residuals and ensuring a good control on each partial model before adding new data corresponding to deeper layers. Finally, we discuss the parallel performance of the code in this particular synthetic case.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Scott I.

As detonation is a coupled fluid-chemical process, flow divergence inside the detonation reaction zone can strongly influence detonation velocity and energy release. Such divergence is responsible for the diameter-effect and failure-diameter phenomena in condensed-phase explosives and particularly dominant in detonation of nonideal explosives such as Ammonium Nitrate and Fuel Oil (ANFO). In this study, the effect of reaction zone flow divergence on ANFO detonation was explored through variation of the inert confinement and explosive diameter in the rate-stick geometry with cylinder expansion experiments. New tests are discussed and compared to prior experiments. Presented results include the detonation velocity as amore » function of diameter and confinement, reaction zone times, detonation product isentropes and energies, as well as sonic surface pressures and velocities. Product energy densities and isentropes were found to increase with detonation velocity, indicating more complete chemical reaction with increased detonation velocity. In addition, detonation reaction zone times were found to scale with the acoustic transit time of the confiner wall and used to show that the ANFO diameter effect scaled with the reaction zone time for a particle along the flow centerline, regardless of the confinement. Such a result indicates that the ANFO reaction mechanisms are sufficiently slow that the centerline fluid expansion timescale is a limiting factor controlling detonation velocity and energy release.« less

Variations in magmatic processes along the East Greenland volcanic margin

NASA Astrophysics Data System (ADS)

Voss, Max; Schmidt-Aursch, Mechita C.; Jokat, Wilfried

2009-05-01

Seismic velocities and the associated thicknesses of rifted and igneous crust provide key constraints on the rifting history, the differentiation between non-volcanic and volcanic rifted margins, the driving force of magmatism at volcanic margins, that is, active or passive upwelling and the temperature anomaly in the lithosphere. This paper presents two new wide-angle seismic transects of the East Greenland margin and combines the velocity models with a compilation of 30-wide-angle seismic velocity models from several publications along the entire East Greenland margin. Compiled maps show the depth to basement, depth to Moho, crustal thickness and thickness of high velocity lower crust (HVLC; with velocities above 7.0 km s-1). First, we present two new wide-angle seismic transects, which contribute to the compilation at the northeast Greenland margin and over the oceanic crust between Shannon Island and the Greenland Fracture Zone. Velocity models, produced by ray tracing result in total traveltime rms-misfits of 100-120 milliseconds and χ2 values of 3.7 and 2.3 for the northern and southern profiles with respect to the data quality and structural complexity. 2-D gravity modelling is used to verify the structural and lithologic constraints. The northernmost profile, AWI-20030200, reveals a magma starved break-up and a rapidly thinning oceanic crust until magnetic anomaly C21 (47.1 Ma). The southern seismic transect, AWI-20030300, exhibits a positive velocity anomaly associated with the Shannon High, and a basin of up to 15 km depth beneath flood basalts between Shannon Island and the continent-ocean boundary. Break-up is associated with minor crustal thickening and a rapidly decreasing thickness of oceanic crust out to anomaly C21. The continental region is proposed to be only sparsely penetrated by volcanism and not underplated by magmatic material at all compared to the vast amount of magmatism further south. Break-up is proposed to have occurred at the seaward boundaries of the continent-ocean transition zones at between ~50 and ~54 Ma, propagating from north to south based on a joint analysis incorporating transects from the Kejser Franz Joseph Fjord and Godthåb Gulf. Secondly, the variation of the HVLC along the East Greenland margin from 60° to 77°N and from transects of its conjugate margin shows inverted emplacement of prominent landward and seaward HVLC thickness portions from north to south in a distribution chart. The differences in the HVLC distribution are attributed to one or more of the following three models. In the first model it is inferred that a transfer zone/detachment acts as a barrier to northward magma flow. In the second model, underplating results in thicker and highly intruded lower crust with several small-scale feeder dykes that locally increase the lower crustal velocities. In the third model, a second magmatic event associated with the separation of the Jan Mayen microcontinent is considered. Lithospheric-scale inhomogeneities might be responsible for the heterogeneous melt generation, the inversion of the HVLC distribution in continental and oceanic domains and differences in its velocities.

Coupled nonlinear drift and ion acoustic waves in dense dissipative electron-positron-ion magnetoplasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masood, W.; Siddiq, M.; Karim, S.

2009-11-15

Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous electron-positron-ion (e-p-i) quantum magnetoplasma with neutrals in the background using the well known quantum hydrodynamic model. In this regard, Korteweg-de Vries-Burgers (KdVB) and Kadomtsev-Petviashvili-Burgers (KPB) equations are obtained. Furthermore, the solutions of KdVB and KPB equations are presented by using the tangent hyperbolic (tanh) method. The variation in the shock profile with the quantum Bohm potential, collision frequency, and the ratio of drift to shock velocity in the comoving frame, v{sub *}/u, is also investigated. It is found that increasing the positron concentration and collisionmore » frequency decreases the strength of the shock. It is also shown that when the localized structure propagates with velocity greater than the diamagnetic drift velocity (i.e., u>v{sub *}), the shock strength decreases. However, the shock strength is observed to increase when the localized structure propagates with velocity less than that of drift velocity (i.e., u

Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

NASA Astrophysics Data System (ADS)

Karstensen, Johannes; Schütte, Florian; Pietri, Alice; Krahmann, Gerd; Fiedler, Björn; Grundle, Damian; Hauss, Helena; Körtzinger, Arne; Löscher, Carolin R.; Testor, Pierre; Vieira, Nuno; Visbeck, Martin

2017-04-01

The temporal evolution of the physical and biogeochemical structure of an oxygen-depleted anticyclonic modewater eddy is investigated over a 2-month period using high-resolution glider and ship data. A weakly stratified eddy core (squared buoyancy frequency N2 ˜ 0.1 × 10-4 s-2) at shallow depth is identified with a horizontal extent of about 70 km and bounded by maxima in N2. The upper N2 maximum (3-5 × 10-4 s-2) coincides with the mixed layer base and the lower N2 maximum (0.4 × 10-4 s-2) is found at about 200 m depth in the eddy centre. The eddy core shows a constant slope in temperature/salinity (T/S) characteristic over the 2 months, but an erosion of the core progressively narrows down the T/S range. The eddy minimal oxygen concentrations decreased by about 5 µmol kg-1 in 2 months, confirming earlier estimates of oxygen consumption rates in these eddies. Separating the mesoscale and perturbation flow components reveals oscillating velocity finestructure ( ˜ 0.1 m s-1) underneath the eddy and at its flanks. The velocity finestructure is organized in layers that align with layers in properties (salinity, temperature) but mostly cross through surfaces of constant density. The largest magnitude in velocity finestructure is seen between the surface and 140 m just outside the maximum mesoscale flow but also in a layer underneath the eddy centre, between 250 and 450 m. For both regions a cyclonic rotation of the velocity finestructure with depth suggests the vertical propagation of near-inertial wave (NIW) energy. Modification of the planetary vorticity by anticyclonic (eddy core) and cyclonic (eddy periphery) relative vorticity is most likely impacting the NIW energy propagation. Below the low oxygen core salt-finger type double diffusive layers are found that align with the velocity finestructure. Apparent oxygen utilization (AOU) versus dissolved inorganic nitrate (NO3-) ratios are about twice as high (16) in the eddy core compared to surrounding waters (8.1). A large NO3- deficit of 4 to 6 µmol kg-1 is determined, rendering denitrification an unlikely explanation. Here it is hypothesized that the differences in local recycling of nitrogen and oxygen, as a result of the eddy dynamics, cause the shift in the AOU : NO3- ratio. High NO3- and low oxygen waters are eroded by mixing from the eddy core and entrain into the mixed layer. The nitrogen is reintroduced into the core by gravitational settling of particulate matter out of the euphotic zone. The low oxygen water equilibrates in the mixed layer by air-sea gas exchange and does not participate in the gravitational sinking. Finally we propose a mesoscale-submesoscale interaction concept where wind energy, mediated via NIWs, drives nutrient supply to the euphotic zone and drives extraordinary blooms in anticyclonic mode-water eddies.

Auditory mechanics in a bush-cricket: direct evidence of dual sound inputs in the pressure difference receiver

PubMed Central

Montealegre-Z, Fernando; Soulsbury, Carl D.; Robson Brown, Kate A.; Robert, Daniel

2016-01-01

The ear of the bush-cricket, Copiphora gorgonensis, consists of a system of paired eardrums (tympana) on each foreleg. In these insects, the ear is backed by an air-filled tube, the acoustic trachea (AT), which transfers sound from the prothoracic acoustic spiracle to the internal side of the eardrums. Both surfaces of the eardrums of this auditory system are exposed to sound, making it a directionally sensitive pressure difference receiver. A key feature of the AT is its capacity to reduce the velocity of sound propagation and alter the acoustic driving forces at the tympanum. The mechanism responsible for reduction in sound velocity in the AT remains elusive, yet it is deemed to depend on adiabatic or isothermal conditions. To investigate the biophysics of such multiple input ears, we used micro-scanning laser Doppler vibrometry and micro-computed X-ray tomography. We measured the velocity of sound propagation in the AT, the transmission gains across auditory frequencies and the time-resolved mechanical dynamics of the tympanal membranes in C. gorgonensis. Tracheal sound transmission generates a gain of approximately 15 dB SPL, and a propagation velocity of ca 255 m s−1, an approximately 25% reduction from free field propagation. Modelling tracheal acoustic behaviour that accounts for thermal and viscous effects, we conclude that reduction in sound velocity within the AT can be explained, among others, by heat exchange between the sound wave and the tracheal walls. PMID:27683000

Thermal Theory of Combustion and Explosion. 3; Theory of Normal Flame Propagation

NASA Technical Reports Server (NTRS)

Semenov, N. N.

1942-01-01

The technical memorandum covers experimental data on flame propagation, the velocity of flame propagation, analysis of the old theoretical views of flame propagation, confirmation of the theory for simple reactions (theory of combustion of explosive substances and in particular nitroglycol), and check of the theory by example of a chain oxidizing reaction (theory of flame propagation in carbon monoxide, air and carbon monoxide - oxygen mixtures).

Geochemical and Depth Variations at the Galápagos 93.25˚W Propagating Rift

NASA Astrophysics Data System (ADS)

Rotella, M.; Sinton, J.; Mahoney, J.; Chazey, W.

2006-12-01

The 93.25°W propagating rift on the Galápagos Spreading Center (GSC) differs markedly from the better-known propagator at 95.5°W in having the morphology of a classic overlapping spreading center (~24 km of overlap and 7.5 km of offset). It has a higher propagation rate (70 vs 48 mm/yr) [Wilson & Hey, JGR v. 100, 1995] and is breaking through younger crust (260 vs 910 ka); overall magma supply is ~20% greater, as the area is closer to the Galápagos hotspot. The overlapping limbs lack pronounced bathymetric lows, instead they are up to 150 m shallower than the surrounding axial ridges away from the offset. Lavas are T-MORB; failing rift lavas show a slight increase in Mg within the overlap zone but propagating rift lavas lack the strong fractionation anomaly that characterizes the propagating limb at 95.5°W and many other propagating rifts. New major and trace element data on 28 samples from 24 dredge stations along a 175 km section of the GSC spanning the 93.25°W offset indicate significant, systematic variations in mantle sources and melting processes on each limb of the system. Fractionation-corrected ratios of highly to moderately incompatible elements (e.g. La/Yb, Sm/Yb, Zr/Y) show constant values along the propagating rift east of 93.2°W, but within the overlap zone these ratios increase sharply up to a factor of 1.5, then gradually decline to the west. In contrast, the failing rift shows constant to moderately increasing ratios as the overlap zone is approached from the west, with lower overall ratios within the zone. These variations could be interpreted to reflect a counter-intuitive relationship of gradually increasing extent of partial melting with progressive failure of the dying rift, consistent with the striking shoaling of the failing limb, or melting of incompatible-element depleted mantle. Variations along the eastern, propagating rift suggest either a sharp decrease in extent of melting or tapping of a more incompatible-element-enriched mantle source within the overlap zone. Limited Nd-Pb-Sr isotopic data suggest source variations are required in addition to variations in extent of melting. Thus, in contrast to other well-documented propagators where geochemical variations are dominated by magma chamber effects, variations around the 93.25°W system appear to be dominated by melting and source.

Effect of the secondary process on mass point vibration velocity propagation in magneto-acoustic tomography and magneto-acousto-electrical tomography.

PubMed

Sun, Zhishen; Liu, Guoqiang; Guo, Liang; Xia, Hui; Wang, Xinli

2016-04-29

As two of the new biological electrical impedance tomography (EIT), magneto-acoustic tomography (MAT) and magneto-acousto-electrical tomography (MAET) achieve both the high contrast property of EIT and the high spatial resolution property of sonography through combining EIT and sonography. As both MAT and MAET contain a uniform magnetic field, vibration and electrical current density, there is a secondary process both in MAT and in MAET, which is MAET and MAT respectively. To analyze the effect of the secondary process on mass point vibration velocity (MPVV) propagation in MAT and MAET. By analyzing the total force to the sample, the wave equations of MPVV in MAT and MAET - when the secondary processes were considered - were derived. The expression of the attenuation constant in the wave number was derived in the case that the mass point vibration velocity propagates in the form of cylindrical wave and plane wave. Attenuations of propagation of the MPVV in several samples were quantified. Attenuations of the MPVV after propagating for 1 mm in copper or aluminum foil, and for 5 cm in gel phantom or biological soft tissue were less than 1%. Attenuations of the MPVV in MAT and MAET due to the secondary processes are relatively minor, and effects of the secondary processes on MPVV propagation in MAT and MAET can be ignored.

40 CFR 146.33 - Operating, monitoring, and reporting requirements.

Code of Federal Regulations, 2014 CFR

2014-07-01

... injection zone during injection does not initiate new fractures or propagate existing fractures in the injection zone. In no case, shall injection pressure initiate fractures in the confining zone or cause the...

40 CFR 146.33 - Operating, monitoring, and reporting requirements.

Code of Federal Regulations, 2013 CFR

2013-07-01

... injection zone during injection does not initiate new fractures or propagate existing fractures in the injection zone. In no case, shall injection pressure initiate fractures in the confining zone or cause the...

40 CFR 146.33 - Operating, monitoring, and reporting requirements.

Code of Federal Regulations, 2010 CFR

2010-07-01

... injection zone during injection does not initiate new fractures or propagate existing fractures in the injection zone. In no case, shall injection pressure initiate fractures in the confining zone or cause the...

40 CFR 146.33 - Operating, monitoring, and reporting requirements.

Code of Federal Regulations, 2011 CFR

2011-07-01

... injection zone during injection does not initiate new fractures or propagate existing fractures in the injection zone. In no case, shall injection pressure initiate fractures in the confining zone or cause the...

40 CFR 146.33 - Operating, monitoring, and reporting requirements.

Code of Federal Regulations, 2012 CFR

2012-07-01

... injection zone during injection does not initiate new fractures or propagate existing fractures in the injection zone. In no case, shall injection pressure initiate fractures in the confining zone or cause the...

Multiple mantle upwellings through the transition zone beneath the Afar Depression?

NASA Astrophysics Data System (ADS)

Hammond, J. O.; Kendall, J. M.; Stuart, G. W.; Thompson, D. A.; Ebinger, C. J.; Keir, D.; Ayele, A.; Goitom, B.; Ogubazghi, G.

2012-12-01

Previous seismic studies using regional deployments of sensors in East-Africa show that low seismic velocities underlie Africa, but their resolution is limited to the top 200-300km of the Earth. Thus, the connection between the low velocities in the uppermost mantle and those imaged in global studies in the lower mantle is unclear. We have combined new data from Afar, Ethiopia with 7 other regional experiments and global network stations across Kenya, Ethiopia, Eritrea, Djibouti and Yemen, to produce high-resolution models of upper mantle P- and S-wave velocities to the base of the transition zone. Relative travel time tomographic inversions show that within the transition zone two focussed sharp-sided low velocity regions exist: one beneath the Western Ethiopian plateau outside the rift valley, and the other beneath the Afar depression. Estimates of transition zone thickness suggest that this is unlikely to be an artefact of mantle discontinuity topography as a transition zone of normal thickness underlies the majority of Afar and surrounding regions. However, a low velocity layer is evident directly above the 410 discontinuity, co-incident with some of the lowest seismic velocities suggesting that smearing of a strong low velocity layer of limited depth extent may contribute to the tomographic models in north-east Afar. The combination of seismic constraints suggests that small low temperature (<50K) upwellings may rise from a broader low velocity plume-like feature in the lower mantle. This interpretation is supported by numerical and analogue experiments that suggest the 660km phase change and viscosity jump may impede flow from the lower to upper mantle creating a thermal boundary layer at the base of the transition zone. This allows smaller, secondary upwellings to initiate and rise to the surface. These, combined with possible evidence of melt above the 410 discontinuity can explain the seismic velocity models. Our images of secondary upwellings suggest that there is no evidence for a plume in the classical sense (i.e. a narrow conduit). Instead, we propose that secondary upwellings rise from the base of the transition zone and connect with the northeast flowing African superswell in the upper mantle.

Ambient noise tomography reveals upper crustal structure of Icelandic rifts

NASA Astrophysics Data System (ADS)

Green, Robert G.; Priestley, Keith F.; White, Robert S.

2017-05-01

The structure of oceanic spreading centres and subsurface melt distribution within newly formed crust is largely understood from marine seismic experiments. In Iceland, however, sub-aerial rift elevation allows both accurate surface mapping and the installation of large broadband seismic arrays. We present a study using ambient noise Rayleigh wave tomography to image the volcanic spreading centres across Iceland. Our high resolution model images a continuous band of low seismic velocities, parallelling all three segments of the branched rift in Iceland. The upper 10 km contains strong velocity variations, with shear wave velocities 0.5 km s-1 faster in the older non-volcanically active regions compared to the active rifts. Slow velocities correlate very closely with geological surface mapping, with contours of the anomalies parallelling the edges of the neo-volcanic zones. The low-velocity band extends to the full 50 km width of the neo-volcanic zones, demonstrating a significant contrast with the narrow (8 km wide) magmatic zone seen at fast spreading ridges, where the rate of melt supply is similarly high. Within the seismically slow rift band, the lowest velocity cores of the anomalies occur above the centre of the mantle plume under the Vatnajökull icecap, and in the Eastern Volcanic Zone under the central volcano Katla. This suggests localisation of melt accumulation at these specific volcanic centres, demonstrating variability in melt supply into the shallow crust along the rift axis. Shear velocity inversions with depth show that the strongest velocity contrasts are found in the upper 8 km, and show a slight depression in the shear velocity through the mid crust (10-20 km) in the rifts. Our model also shows less intensity to the slow rift anomaly in the Western Volcanic Zone, supporting the notion that rift activity here is decreasing as the ridge jumps to the Eastern Volcanic Zone.

Atomic-level deformation of CuxZr100-x metallic glasses under shock loading

NASA Astrophysics Data System (ADS)

Demaske, Brian J.; Wen, Peng; Phillpot, Simon R.; Spearot, Douglas E.

2018-06-01

Plastic deformation mechanisms in CuxZr100-x bulk metallic glasses (MGs) subjected to shock are investigated using molecular dynamics simulations. MGs with Cu compositions between 30 and 70 at. % subjected to shock waves generated via piston velocities that range from 0.125 to 2.0 km/s are considered. In agreement with prior studies, plastic deformation is initiated via formation of localized regions of high von Mises shear strain, known as shear transformation zones (STZs). At low impact velocities, but above the Hugoniot elastic limit, STZ nucleation is dispersed behind the shock front. As impact velocity is increased, STZ nucleation becomes more homogeneous, eventually leading to shock-induced melting, which is identified in this work via high atomic diffusivity. The shear stress necessary to initiate plastic deformation within the shock front is independent of composition at shock intensities near the elastic limit but increases with increasing Cu content at high shock intensities. By contrast, both the flow stress in the plastically deformed MG and the critical shock pressure associated with melting behind the shock front are found to increase with increasing Cu content over the entire range of impact velocities. The evolution of the short-range order in the MG samples during shock wave propagation is analyzed using a polydisperse Voronoi tessellation method. Cu-centered polyhedra with full icosahedral symmetry are found to be most resistant to change under shock loading independent of the MG composition. A saturation is observed in the involvement of select Cu-centered polyhedra in the plastic deformation processes at a piston velocity around 0.75 km/s.

Seismic velocity structure in the western part of Nankai subduction zone

NASA Astrophysics Data System (ADS)

Yamamoto, Y.; Obana, K.; Takahashi, T.; Nakanishi, A.; Kodaira, S.; Kaneda, Y.

2011-12-01

In the Nankai Trough, three major seismogenic zones of megathrust earthquake exist (Tokai, Tonankai and Nankai earthquake regions). The Hyuga-nada region was distinguished from these seismogenic zones because of the lack of megathrust earthquake. However, recent studies show the possibility of simultaneous rupture of the Nankai and Hyuga-nada segments was also pointed out [e.g., Furumura et al, 2010 JGR]. Because seismic velocity structure is one of the useful and basic information for understanding the possibility of seismic linkage of Nankai and Hyuga-nada segments, Japan Agency for Marine-Earth Science and Technology has been carried out a series of wide-angle active source surveys and local seismic observations among the three major seismogenic zones and Hyuga-nada segment from 2008, as a part of "Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan". We are performing two set of three-dimensional seismic velocity tomographic inversions, one is in the Hyuga-nada region and the other is western part of the coseismic rupture area of 1946 Nankai earthquake, to discuss the relationship between the structural heterogeneities and the location of segment boundary between Hyuga-nada and Nankai segment. For the analysis of Hyuga-nada segment, we used both active and passive source data. The obtained velocity model clearly showed the subducted Kyushu-Palau ridge as thick low velocity Philippine Sea slab in the southwestern part. Our velocity image also indicates that "the thin oceanic crust zone" located between Nankai segment and Kyushu-Palau Ridge segment, founded by Nakanishi et al [2010, AGU] by analyzing of the active source survey, continuously exists from trough axis to near the coastline of Kyushu Island. The overriding plate just above the coseismic slip area of 1968 Hyuga-nada earthquake shows relatively high velocity. Although the tomographic study in the western part of Nankai seismogenic zone is still a preliminary stage and we used only a part of the passive source data, we found the anomalous high velocity zone in the overriding plate. This zone is located at just beneath the cape Ashizuri, corresponding to the boundary between the Nankai and Hyuga-nada segments. To clarify more detail structure, we will perform the joint inversion using both active and passive source data in the western Nankai seismogenic zone.

Reexamination of group velocities of structured light pulses

NASA Astrophysics Data System (ADS)

Saari, Peeter

2018-06-01

Recently, a series of theoretical and experimental papers on free-space propagation of pulsed Laguerre-Gaussian and Bessel beams was published, which reached contradictory and controversial results about group velocities of such pulses. Depending on the measurement scheme, the group velocity can be defined differently. We analyze how different versions of group velocity are related to the measurable travel time (time of flight) of the pulse between input (source) and output (detecting) planes. The analysis is tested on a theoretical model—the Bessel-Gauss pulse whose propagation path exhibits both subluminal and superluminal regions. Our main conclusion from resolving the contradictions in the literature is that different versions of group velocity are appropriate, depending on whether or not the beam is hollow and how the pulse is recorded in the output plane—integrally or with spatial resolution.

Seismic velocity change and slip rate during the 2006 Guerrero (Mexico) slow slip event

NASA Astrophysics Data System (ADS)

Rivet, Diane; Radiguet, Mathilde; Campillo, Michel; Cotton, Fabrice; Shapiro, Nikolai; Krishna Singh, Shri; Kostoglodov, Vladimir

2010-05-01

We measure temporal change of the seismic velocity in the crust below the Guerrero region during the 2006 slow sleep event (SSE). We use repeated cross-correlations of ambient seismic noise recorded at 26 broad-band stations of the MesoAmerica Seismic Experiment (MASE). The cross-correlations are computed over 90 days with a moving window of 10 days from January 2005 to July 2007. To insure measurements independent of noise source variations, we only take into account the travel time change within the coda. For period of 8 to 20s, we observe a decrease in velocity starting in April 2006 with a maximum change of -0.3% of the initial velocity in June 2006. At these periods, the Rayleigh waves are sensitive to velocity changes down to the lower crust. In the other hand, we compute the deformation rate below the MASE array from a slip propagation model of the SSE observed by means of the displacement time-series of 15 continuous GPS stations. Slip initiates in the western part of the Guerrero Gap and propagates southeastward. The propagation velocity is of the order of 1 km/day. We then compare the seismic velocity change measured from continuous seismological data with the deformation rate inferred from geodetic measurements below the MASE array. We obtain a good agreement between the time of maximal seismic velocity change (July 2006) and the time of maximum deformation associated with the SSE (July to August 2006). This result shows that the long-term velocity change associated with the SSE can be detected using continuous seismic recordings. Since the SSE does not emit seismic waves, which interact with the superficial layers, the result indicates that the velocity change is due to deformation at depth.

Stress waves in transversely isotropic media: The homogeneous problem

NASA Technical Reports Server (NTRS)

Marques, E. R. C.; Williams, J. H., Jr.

1986-01-01

The homogeneous problem of stress wave propagation in unbounded transversely isotropic media is analyzed. By adopting plane wave solutions, the conditions for the existence of the solution are established in terms of phase velocities and directions of particle displacements. Dispersion relations and group velocities are derived from the phase velocity expressions. The deviation angles (e.g., angles between the normals to the adopted plane waves and the actual directions of their propagation) are numerically determined for a specific fiber-glass epoxy composite. A graphical method is introduced for the construction of the wave surfaces using magnitudes of phase velocities and deviation angles. The results for the case of isotropic media are shown to be contained in the solutions for the transversely isotropic media.

Analytical and Numerical Modeling of Tsunami Wave Propagation for double layer state in Bore

NASA Astrophysics Data System (ADS)

Yuvaraj, V.; Rajasekaran, S.; Nagarajan, D.

2018-04-01

Tsunami wave enters into the river bore in the landslide. Tsunami wave propagation are described in two-layer states. The velocity and amplitude of the tsunami wave propagation are calculated using the double layer. The numerical and analytical solutions are given for the nonlinear equation of motion of the wave propagation in a bore.

Principal curvatures and area ratio of propagating surfaces in isotropic turbulence

NASA Astrophysics Data System (ADS)

Zheng, Tianhang; You, Jiaping; Yang, Yue

2017-10-01

We study the statistics of principal curvatures and the surface area ratio of propagating surfaces with a constant or nonconstant propagating velocity in isotropic turbulence using direct numerical simulation. Propagating surface elements initially constitute a plane to model a planar premixed flame front. When the statistics of evolving propagating surfaces reach the stationary stage, the statistical profiles of principal curvatures scaled by the Kolmogorov length scale versus the constant displacement speed scaled by the Kolmogorov velocity scale collapse at different Reynolds numbers. The magnitude of averaged principal curvatures and the number of surviving surface elements without cusp formation decrease with increasing displacement speed. In addition, the effect of surface stretch on the nonconstant displacement speed inhibits the cusp formation on surface elements at negative Markstein numbers. In order to characterize the wrinkling process of the global propagating surface, we develop a model to demonstrate that the increase of the surface area ratio is primarily due to positive Lagrangian time integrations of the area-weighted averaged tangential strain-rate term and propagation-curvature term. The difference between the negative averaged mean curvature and the positive area-weighted averaged mean curvature characterizes the cellular geometry of the global propagating surface.

The Inhomogeneous Waves in a Rotating Piezoelectric Body

PubMed Central

Chen, Si

2013-01-01

This paper presents the analysis and numerical results of rotation, propagation angle, and attenuation angle upon the waves propagating in the piezoelectric body. Via considering the centripetal and Coriolis accelerations in the piezoelectric equations with respect to a rotating frame of reference, wave velocities and attenuations are derived and plotted graphically. It is demonstrated that rotation speed vector can affect wave velocities and make the piezoelectric body behaves as if it was damping. Besides, the effects of propagation angle and attenuation angle are presented. Critical point is found when rotation speed is equal to wave frequency, around which wave characteristics change drastically. PMID:24298219

Predicting propagation limits of laser-supported detonation by Hugoniot analysis

NASA Astrophysics Data System (ADS)

Shimamura, Kohei; Ofosu, Joseph A.; Komurasaki, Kimiya; Koizumi, Hiroyuki

2015-01-01

Termination conditions of a laser-supported detonation (LSD) wave were investigated using control volume analysis with a Shimada-Hugoniot curve and a Rayleigh line. Because the geometric configurations strongly affect the termination condition, a rectangular tube was used to create the quasi-one-dimensional configuration. The LSD wave propagation velocity and the pressure behind LSD were measured. Results reveal that the detonation states during detonation and at the propagation limit are overdriven detonation and Chapman-Jouguet detonation, respectively. The termination condition is the minimum velocity criterion for the possible detonation solution. Results were verified using pressure measurements of the stagnation pressure behind the LSD wave.

Long-term variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric gravity waves by using airglow images obtained at Shigarkai, Japan

NASA Astrophysics Data System (ADS)

Takeo, D.; Kazuo, S.; Hujinami, H.; Otsuka, Y.; Matsuda, T. S.; Ejiri, M. K.; Yamamoto, M.; Nakamura, T.

2016-12-01

Atmospheric gravity waves generated in the lower atmosphere transport momentum into the upper atmosphere and release it when they break. The released momentum drives the global-scale pole-to-pole circulation and causes global mass transport. Vertical propagation of the gravity waves and transportation of momentum depend on horizontal phase velocity of gravity waves according to equation about dispersion relation of waves. Horizontal structure of gravity waves including horizontal phase velocity can be seen in the airglow images, and there have been many studies about gravity waves by using airglow images. However, long-term variation of horizontal phase velocity spectrum of gravity waves have not been studied yet. In this study, we used 3-D FFT method developed by Matsuda et al., (2014) to analyze the horizontal phase velocity spectrum of gravity waves by using 557.7-nm (altitude of 90-100 km) and 630.0-nm (altitude of 200-300 km) airglow images obtained at Shigaraki MU Observatory (34.8 deg N, 136.1 deg E) over 16 years from October 1, 1998 to July 26, 2015. Results about 557.7-nm shows clear seasonal variation of propagation direction of gravity waves in the mesopause region. Between summer and winter, there are propagation direction anisotropies which probably caused by filtering due to zonal mesospheric jet and by difference of latitudinal location of wave sources relative to Shigaraki. Results about 630.0-nm shows clear negative correlation between the yearly power spectrum density of horizontal phase velocity and sunspot number. This negative correlation with solar activity is consistent with growth rate of the Perkins instability, which may play an important role in generating the nighttime medium-scale traveling ionospheric disturbances at middle latitudes.

Molecular-dynamics Simulation-based Cohesive Zone Representation of Intergranular Fracture Processes in Aluminum

NASA Technical Reports Server (NTRS)

Yamakov, Vesselin I.; Saether, Erik; Phillips, Dawn R.; Glaessgen, Edward H.

2006-01-01

A traction-displacement relationship that may be embedded into a cohesive zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum cohesive zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent cohesive zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation

Foreshocks and aftershocks of Pisagua 2014 earthquake: time and space evolution of megathrust event.

NASA Astrophysics Data System (ADS)

Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Wollam, Jack; Thomas, Reece; de Lima Neto, Oscar; Tavera, Hernando; Garth, Thomas; Ruiz, Sergio

2016-04-01

The 2014 Pisagua earthquake of magnitude 8.2 is the first case in Chile where a foreshock sequence was clearly recorded by a local network, as well all the complete sequence including the mainshock and its aftershocks. The seismicity of the last year before the mainshock include numerous clusters close to the epicentral zone (Ruiz et al; 2014) but it was on 16th March that this activity became stronger with the Mw 6.7 precursory event taking place in front of Iquique coast at 12 km depth. The Pisagua earthquake arrived on 1st April 2015 breaking almost 120 km N-S and two days after a 7.6 aftershock occurred in the south of the rupture, enlarging the zone affected by this sequence. In this work, we analyse the foreshocks and aftershock sequence of Pisagua earthquake, from the spatial and time evolution for a total of 15.764 events that were recorded from the 1st March to 31th May 2015. This event catalogue was obtained from the automatic analyse of seismic raw data of more than 50 stations installed in the north of Chile and the south of Peru. We used the STA/LTA algorithm for the detection of P and S arrival times on the vertical components and then a method of back propagation in a 1D velocity model for the event association and preliminary location of its hypocenters following the algorithm outlined by Rietbrock et al. (2012). These results were then improved by locating with NonLinLoc software using a regional velocity model. We selected the larger events to analyse its moment tensor solution by a full waveform inversion using ISOLA software. In order to understand the process of nucleation and propagation of the Pisagua earthquake, we also analysed the evolution in time of the seismicity of the three months of data. The zone where the precursory events took place was strongly activated two weeks before the mainshock and remained very active until the end of the analysed period with an important quantity of the seismicity located in the upper plate and having variations in its focal mechanisms. The evolution of the Pisagua sequence point out a rupture by steps, that we suggest to be related to the properties of the upper plate, as well as along in the subduction interface. The spatial distribution of seismicity was compared to the inter-seismic coupling of previous studies, the regional bathymetry and the slip distribution of both the mainshock and the Magnitude 7.6 event. The results show an important relation between the low coupling zones and the areas lacking large magnitude events

Passive turbulent flamelet propagation

NASA Technical Reports Server (NTRS)

Ashurst, William T.; Ruetsch, G. R.; Lund, T. S.

1994-01-01

We analyze results of a premixed constant density flame propagating in three-dimensional turbulence, where a flame model developed by Kerstein, et al. (1988) has been used. Simulations with constant and evolving velocity fields are used, where peculiar results were obtained from the constant velocity field runs. Data from the evolving flow runs with various flame speeds are used to determine two-point correlations of the fluctuating scalar field and implications for flamelet modeling are discussed.

Wave propagation in fluid-conveying viscoelastic single-walled carbon nanotubes with surface and nonlocal effects

NASA Astrophysics Data System (ADS)

Zhen, Ya-Xin

2017-02-01

In this paper, the transverse wave propagation in fluid-conveying viscoelastic single-walled carbon nanotubes is investigated based on nonlocal elasticity theory with consideration of surface effect. The governing equation is formulated utilizing nonlocal Euler-Bernoulli beam theory and Kelvin-Voigt model. Explicit wave dispersion relation is developed and wave phase velocities and frequencies are obtained. The effect of the fluid flow velocity, structural damping, surface effect, small scale effects and tube diameter on the wave propagation properties are discussed with different wave numbers. The wave frequency increases with the increase of fluid flow velocity, but decreases with the increases of tube diameter and wave number. The effect of surface elasticity and residual surface tension is more significant for small wave number and tube diameter. For larger values of wave number and nonlocal parameters, the real part of frequency ratio raises.

Flying Focus: Spatiotemporal Control of the Laser Beam Intensity

NASA Astrophysics Data System (ADS)

Froula, D. H.; Turnbull, D.; Kessler, T. J.; Haberberger, D.; Bahk, S.-W.; Begishev, I. A.; Boni, R.; Bucht, S.; Davies, A.; Katz, J.; Sefkow, A. B.; Shaw, J. L.

2017-10-01

A ``flying focus'' is presented: this advanced focusing scheme provides unprecedented spatiotemporal control over the laser focal volume. A chromatic focusing system combined with chirped laser pulses enabled the speed of a small-diameter laser focus to propagate over nearly 100 × its Rayleigh length. Furthermore, the flying focus decouples the speed at which the peak intensity propagates from the group velocity of the laser pulse, allowing the laser focus to co- or counter-propagate along its axis at any velocity. Experiments have demonstrated a nearly constant intensity over 4.5 mm while the velocity of the focus ranged from subluminal (0.01 c) to superluminal (15 c) . These properties could provide the opportunity to overcome current fundamental limitations in laser-plasma amplifiers, laser-wakefield accelerators, photon accelerators, ion accelerators, and high-order frequency conversion. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Hydrodynamic characteristics and overall volumetric oxygen transfer coefficient of a new multi-environment bioreactor.

PubMed

Behzadian, Farnaz; Yerushalmi, Laleh; Alimahmoodi, Mahmood; Mulligan, Catherine N

2013-08-01

The hydrodynamic characteristics and the overall volumetric oxygen transfer coefficient of a new multi-environment bioreactor which is an integrated part of a wastewater treatment system, called BioCAST, were studied. This bioreactor contains several zones with different environmental conditions including aerobic, microaerophilic and anoxic, designed to increase the contaminant removal capacity of the treatment system. The multi-environment bioreactor is designed based on the concept of airlift reactors where liquid is circulated through the zones with different environmental conditions. The presence of openings between the aerobic zone and the adjacent oxygen-depleted microaerophilic zone changes the hydrodynamic properties of this bioreactor compared to the conventional airlift designs. The impact of operating and process parameters, notably the hydraulic retention time (HRT) and superficial gas velocity (U(G)), on the hydrodynamics and mass transfer characteristics of the system was examined. The results showed that liquid circulation velocity (V(L)), gas holdup (ε) and overall volumetric oxygen transfer coefficient (k(L)a(L)) increase with the increase of superficial gas velocity (U(G)), while the mean circulation time (t(c)) decreases with the increase of superficial gas velocity. The mean circulation time between the aerobic zone (riser) and microaerophilic zone (downcomer) is a stronger function of the superficial gas velocity for the smaller openings (1/2 in.) between the two zones, while for the larger opening (1 in.) the mean circulation time is almost independent of U(G) for U(G) ≥ 0.023 m/s. The smaller openings between the two zones provide higher mass transfer coefficient and better zone generation which will contribute to improved performance of the system during treatment operations.

A study of the dynamics of seizure propagation across micro domains in the vicinity of the seizure onset zone

PubMed Central

Basu, Ishita; Kudela, Pawel; Korzeniewska, Anna; Franaszczuk, Piotr J.; Anderson, William S.

2015-01-01

Objective The use of micro-electrode arrays to measure electrical activity from the surface of the brain is increasingly being investigated as a means to improve seizure onset zone localization. In this work, we used a multivariate autoregressive model to determine the evolution of seizure dynamics in the 70 – 110 Hz high frequency band across micro-domains sampled by such micro-electrode arrays. Approach We used 7 complex partial seizures recorded from 4 patients undergoing intracranial monitoring for surgical evaluation to reconstruct the seizure propagation pattern over sliding windows using a directed transfer function measure. Main results We showed that a directed transfer function can be used to estimate the flow of seizure activity in a set of simulated micro-electrode data with known propagation pattern. In general, depending on the location of the micro-electrode grid with respect to the clinical seizure onset zone and the time from seizure onset, ictal propagation changed in directional characteristics over a 2 to 10 seconds time scale, with gross directionality limited to spatial dimensions of approximately 9mm2. It was also seen that the strongest seizure patterns in the high frequency band and their sources over such micro-domains are more stable over time and across seizures bordering the clinically determined seizure onset zone than inside. Significance This type of propagation analysis might in future provide an additional tool to epileptologists for characterizing epileptogenic tissue. This will potentially help narrowing down resection zones without compromising essential brain functions as well as provide important information about targeting anti-epileptic stimulation devices. PMID:26061006

Toward the Reliability of Fault Representation Methods in Finite Difference Schemes for Simulation of Shear Rupture Propagation

NASA Astrophysics Data System (ADS)

Dalguer, L. A.; Day, S. M.

2006-12-01

Accuracy in finite difference (FD) solutions to spontaneous rupture problems is controlled principally by the scheme used to represent the fault discontinuity, and not by the grid geometry used to represent the continuum. We have numerically tested three fault representation methods, the Thick Fault (TF) proposed by Madariaga et al (1998), the Stress Glut (SG) described by Andrews (1999), and the Staggered-Grid Split-Node (SGSN) methods proposed by Dalguer and Day (2006), each implemented in a the fourth-order velocity-stress staggered-grid (VSSG) FD scheme. The TF and the SG methods approximate the discontinuity through inelastic increments to stress components ("inelastic-zone" schemes) at a set of stress grid points taken to lie on the fault plane. With this type of scheme, the fault surface is indistinguishable from an inelastic zone with a thickness given by a spatial step dx for the SG, and 2dx for the TF model. The SGSN method uses the traction-at-split-node (TSN) approach adapted to the VSSG FD. This method represents the fault discontinuity by explicitly incorporating discontinuity terms at velocity nodes in the grid, with interactions between the "split nodes" occurring exclusively through the tractions (frictional resistance) acting between them. These tractions in turn are controlled by the jump conditions and a friction law. Our 3D tests problem solutions show that the inelastic-zone TF and SG methods show much poorer performance than does the SGSN formulation. The SG inelastic-zone method achieved solutions that are qualitatively meaningful and quantitatively reliable to within a few percent. The TF inelastic-zone method did not achieve qualitatively agreement with the reference solutions to the 3D test problem, and proved to be sufficiently computationally inefficient that it was not feasible to explore convergence quantitatively. The SGSN method gives very accurate solutions, and is also very efficient. Reliable solution of the rupture time is reached with a median resolution of the cohesive zone of only ~2 grid points, and efficiency is competitive with the Boundary Integral (BI) method. The results presented here demonstrate that appropriate fault representation in a numerical scheme is crucial to reduce uncertainties in numerical simulations of earthquake source dynamics and ground motion, and therefore important to improving our understanding of earthquake physics in general.

Numerical modeling the genetic mechanism of Cenozoic intraplate Volcanoes in Northeastern China

NASA Astrophysics Data System (ADS)

Qu, Wulin; Chen, Yongshun John; Zhang, Huai; Jin, Yimin; Shi, Yaolin

2017-04-01

Changbaishan Volcano located about 1400 km west of Japan Trench is an intra continental volcano which having different origin from island arc volcanoes. A number of different mechanisms have been proposed to interpret the origin of intraplate volcanoes, such as deep mantle plumes, back-arc extension and decompressional partial melting, asthenosphere upwelling and decompressional melting, and deep stagnant slab dehydration and partial melting. The recent geophysical research reveals that the slow seismic velocity anomaly extends continuously just below 660 km depth to surface beneath Changbaishan by seismic images and three-dimensional waveform modelling [Tang et al., 2014]. The subduction-induced upwelling occurs within a gap in the stagnant subducted Pacific Plate and produces decompressional melting. Water in deep Earth can reduce viscosity and lower melting temperature and seismic velocity and has effects on many other physical properties of mantle materials. The water-storage capacity of wadsleyite and ringwoodite, which are the main phase in the mantle transition zone, is much greater than that of upper mantle and lower mantle. Geophysical evidences have shown that water content in the mantle transition zone is exactly greater than that of upper mantle and lower mantle [Karato, 2011]. Subducted slab could make mantle transition zone with high water content upward or downward across main phase change surface to release water, and lead to partial melting. We infer that the partial melting mantle and subducted slab materials propagate upwards and form the Cenozoic intraplate Volcanoes in Northeastern China. We use the open source code ASPECT [Kronbichler et al., 2012] to simulate the formation and migration of magma contributing to Changbaishan Volcano. We find that the water entrained by subducted slab from surface has only small proportion comparing to water content of mantle transition zone. Our model provide insights into dehydration melting induced by water transport out of the mantle transition zone associated with dynamic interactions between the subducted slab and surrounding mantle. References Karato, S. (2011), Water distribution across the mantle transition zone and its implications for global material circulation, EARTH PLANET SC LETT, 301(3), 413-423. Kronbichler, M., et al. (2012), High accuracy mantle convection simulation through modern numerical methods, GEOPHYS J INT, 191(1), 12-29. Tang, Y., et al. (2014), Changbaishan volcanism in northeast China linked to subduction-induced mantle upwelling, NAT GEOSCI, 7(6), 470-475.

Influence of exothermic chemical reactions on laser-induced shock waves.

PubMed

Gottfried, Jennifer L

2014-10-21

Differences in the excitation of non-energetic and energetic residues with a 900 mJ, 6 ns laser pulse (1064 nm) have been investigated. Emission from the laser-induced plasma of energetic materials (e.g. triaminotrinitrobenzene [TATB], cyclotrimethylene trinitramine [RDX], and hexanitrohexaazaisowurtzitane [CL-20]) is significantly reduced compared to non-energetic materials (e.g. sugar, melamine, and l-glutamine). Expansion of the resulting laser-induced shock wave into the air above the sample surface was imaged on a microsecond timescale with a high-speed camera recording multiple frames from each laser shot; the excitation of energetic materials produces larger heat-affected zones in the surrounding atmosphere (facilitating deflagration of particles ejected from the sample surface), results in the formation of additional shock fronts, and generates faster external shock front velocities (>750 m s(-1)) compared to non-energetic materials (550-600 m s(-1)). Non-explosive materials that undergo exothermic chemical reactions in air at high temperatures such as ammonium nitrate and magnesium sulfate produce shock velocities which exceed those of the inert materials but are less than those generated by the exothermic reactions of explosive materials (650-700 m s(-1)). The most powerful explosives produced the highest shock velocities. A comparison to several existing shock models demonstrated that no single model describes the shock propagation for both non-energetic and energetic materials. The influence of the exothermic chemical reactions initiated by the pulsed laser on the velocity of the laser-induced shock waves has thus been demonstrated for the first time.

Distributed sensing of ionospheric irregularities with a GNSS receiver array

NASA Astrophysics Data System (ADS)

Su, Yang; Datta-Barua, Seebany; Bust, Gary S.; Deshpande, Kshitija B.

2017-08-01

We present analysis methods for studying the structuring and motion of ionospheric irregularities at the subkilometer scale sizes that produce L band scintillations. Spaced-receiver methods are used for Global Navigation Satellite System (GNSS) receivers' phase measurements over approximately subkilometer to kilometer length baselines for the first time. The quantities estimated by these techniques are plasma drift velocity, diffraction anisotropy magnitude and orientation, and characteristic velocity. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts through linearization about the estimated values of the state. Five receivers of SAGA, the Scintillation Auroral Global Positioning System (GPS) Array, provide 100 Hz power and phase data for each channel at L1 frequency. The array is sited in the auroral zone at Poker Flat Research Range, Alaska. A case study of a single scintillating satellite observed by the array is used to demonstrate the spaced-receiver and uncertainty estimation process. A second case study estimates drifts as measured by multiple scintillating channels. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30 min period are compared to a collocated incoherent scatter radar and show good agreement in horizontal drift speed and direction during periods of scintillation for which the characteristic velocity is less than the drift velocity.

Active source monitoring at the Wenchuan fault zone: coseismic velocity change associated with aftershock event and its implication

NASA Astrophysics Data System (ADS)

Yang, Wei; Ge, Hongkui; Wang, Baoshan; Hu, Jiupeng; Yuan, Songyong; Qiao, Sen

2014-12-01

With the improvement of seismic observation system, more and more observations indicate that earthquakes may cause seismic velocity change. However, the amplitude and spatial distribution of the velocity variation remains a controversial issue. Recent active source monitoring carried out adjacent to Wenchuan Fault Scientific Drilling (WFSD) revealed unambiguous coseismic velocity change associated with a local M s5.5 earthquake. Here, we carry out forward modeling using two-dimensional spectral element method to further investigate the amplitude and spatial distribution of observed velocity change. The model is well constrained by results from seismic reflection and WFSD coring. Our model strongly suggests that the observed coseismic velocity change is localized within the fault zone with width of ~120 m rather than dynamic strong ground shaking. And a velocity decrease of ~2.0 % within the fault zone is required to fit the observed travel time delay distribution, which coincides with rock mechanical experiment and theoretical modeling.

Front propagation in a regular vortex lattice: Dependence on the vortex structure.

PubMed

Beauvier, E; Bodea, S; Pocheau, A

2017-11-01

We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.

SLOW PATCHY EXTREME-ULTRAVIOLET PROPAGATING FRONTS ASSOCIATED WITH FAST CORONAL MAGNETO-ACOUSTIC WAVES IN SOLAR ERUPTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Y.; Ding, M. D.; Chen, P. F., E-mail: guoyang@nju.edu.cn

2015-08-15

Using the high spatiotemporal resolution extreme ultraviolet (EUV) observations of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we conduct a statistical study of the observational properties of the coronal EUV propagating fronts. We find that it might be a universal phenomenon for two types of fronts to coexist in a large solar eruptive event. It is consistent with the hybrid model of EUV propagating fronts, which predicts that coronal EUV propagating fronts consist of both a fast magneto-acoustic wave and a nonwave component. We find that the morphologies, propagation behaviors, and kinematic features of the two EUVmore » propagating fronts are completely different from each other. The fast magneto-acoustic wave fronts are almost isotropic. They travel continuously from the flaring region across multiple magnetic polarities to global distances. On the other hand, the slow nonwave fronts appear as anisotropic and sequential patches of EUV brightening. Each patch propagates locally in the magnetic domains where the magnetic field lines connect to the bottom boundary and stops at the magnetic domain boundaries. Within each magnetic domain, the velocities of the slow patchy nonwave component are an order of magnitude lower than that of the fast-wave component. However, the patches of the slow EUV propagating front can jump from one magnetic domain to a remote one. The velocities of such a transit between different magnetic domains are about one-third to one-half of those of the fast-wave component. The results show that the velocities of the nonwave component, both within one magnetic domain and between different magnetic domains, are highly nonuniform due to the inhomogeneity of the magnetic field in the lower atmosphere.« less

A general mixture model and its application to coastal sandbar migration simulation

NASA Astrophysics Data System (ADS)

Liang, Lixin; Yu, Xiping

2017-04-01

A mixture model for general description of sediment laden flows is developed and then applied to coastal sandbar migration simulation. Firstly the mixture model is derived based on the Eulerian-Eulerian approach of the complete two-phase flow theory. The basic equations of the model include the mass and momentum conservation equations for the water-sediment mixture and the continuity equation for sediment concentration. The turbulent motion of the mixture is formulated for the fluid and the particles respectively. A modified k-ɛ model is used to describe the fluid turbulence while an algebraic model is adopted for the particles. A general formulation for the relative velocity between the two phases in sediment laden flows, which is derived by manipulating the momentum equations of the enhanced two-phase flow model, is incorporated into the mixture model. A finite difference method based on SMAC scheme is utilized for numerical solutions. The model is validated by suspended sediment motion in steady open channel flows, both in equilibrium and non-equilibrium state, and in oscillatory flows as well. The computed sediment concentrations, horizontal velocity and turbulence kinetic energy of the mixture are all shown to be in good agreement with experimental data. The mixture model is then applied to the study of sediment suspension and sandbar migration in surf zones under a vertical 2D framework. The VOF method for the description of water-air free surface and topography reaction model is coupled. The bed load transport rate and suspended load entrainment rate are all decided by the sea bed shear stress, which is obtained from the boundary layer resolved mixture model. The simulation results indicated that, under small amplitude regular waves, erosion occurred on the sandbar slope against the wave propagation direction, while deposition dominated on the slope towards wave propagation, indicating an onshore migration tendency. The computation results also shows that the suspended load will also make great contributions to the topography change in the surf zone, which is usually neglected in some previous researches.

Crystal plastic earthquakes in dolostones

NASA Astrophysics Data System (ADS)

Passelegue, Francois; Aubry, Jerome; Nicolas, Aurelien; Fondriest, Michele; Schubnel, Alexandre; Di Toro, Giulio

2017-04-01

Dolostone is the most dominant lithology of the seismogenic upper crust around the Mediterranean Sea. Understanding the internal mechanisms controlling fault friction is crucial for understanding seismicity along active faults. Displacement in such fault zones is frequently highlighted by highly reflective (mirror-like) slip surfaces, created by thin films of nanogranular fault rock. Using saw-cut dolostone samples coming from natural fault zones, we conducted friction experiments under triaxial loading conditions. To reproduce the natural conditions, experiments were conducted at 30, 60 and 90 MPa confining pressure at respectively 30, 65 and 100 degrees C. At 30 and 65 degrees C, only slow rupture was observed and the experimental fault exhibits frictional behaviour, i.e. a dependence of normal stress on peak shear stress. At 65 degrees C, a strengthening behaviour is observed after the main rupture, leading to a succession of slow rupture. At 100 degrees C, the macroscopic behaviour of the fault becomes ductile, and no dependence of pressure on the peak shear stress is observed. In addition, the increase of the confining pressure up to 60 and 90 MPa allow the transition from slow to fast rupture, highlighted by the records of acoustic activity and by dynamic stress drop occurring in a few tens of microseconds. Using strain gages located along the fault surface and acoustic transducers, we were able to measure the rupture velocities during slow and fast rupture. Slow ruptures propagated around 0.1 m/s, in agreement with natural observations. Fast ruptures propagated up the supershear velocities, i.e. faster than the shear wave speed (>3500 m/s). A complete study of the microstructures was realized before and after ruptures. Slow ruptures lead to the production of mirror-like surface driven by the production of nanograins due to dislocation processes. Fast ruptures induce the production of amorphous material along the fault surface, which may come from melting processes. We demonstrate that the transition from slow to dynamic instabilities is observed when the entire fault exhibits plastic processes, which increase the stiffness of the fault.

ESP Toolbox: A Computational Framework for Precise, Scale-Independent Analysis of Bulk Elastic and Seismic Properties

NASA Astrophysics Data System (ADS)

Johnson, S. E.; Vel, S. S.; Cook, A. C.; Song, W. J.; Gerbi, C. C.; Okaya, D. A.

2014-12-01

Owing to the abundance of highly anisotropic minerals in the crust, the Voigt and Reuss bounds on the seismic velocities can be separated by more than 1 km/s. These bounds are determined by modal mineralogy and crystallographic preferred orientations (CPO) of the constituent minerals, but where the true velocities lie between these bounds is determined by other fabric parameters such as the shapes, shape-preferred orientations, and spatial arrangements of grains. Thus, the calculation of accurate bulk stiffness relies on explicitly treating the grain-scale heterogeneity, and the same principle applies at larger scales, for example calculating accurate bulk stiffness for a crustal volume with varying proportions and distributions of folds or shear zones. We have developed stand-alone GUI software - ESP Toolbox - for the calculation of 3D bulk elastic and seismic properties of heterogeneous and polycrystalline materials using image or EBSD data. The GUI includes a number of different homogenization techniques, including Voigt, Reuss, Hill, geometric mean, self-consistent and asymptotic expansion homogenization (AEH) methods. The AEH method, which uses a finite element mesh, is most accurate since it explicitly accounts for elastic interactions of constituent minerals/phases. The user need only specify the microstructure and material properties of the minerals/phases. We use the Toolbox to explore changes in bulk elasticity and related seismic anisotropy caused by specific variables, including: (a) the quartz alpha-beta phase change in rocks with varying proportions of quartz, (b) changes in modal mineralogy and CPO fabric that occur during progressive deformation and metamorphism, and (c) shear zones of varying thickness, abundance and geometry in continental crust. The Toolbox allows rapid sensitivity analysis around these and other variables, and the resulting bulk stiffness matrices can be used to populate volumes for synthetic wave propagation experiments that allow direct visualization of how variables of interest might affect propagation at a variety of scales. Sensitivity analyses also illustrate the value of the more precise AEH method. The ESP Toolbox can be downloaded here: http://umaine.edu/mecheng/faculty-and-staff/senthil-vel/software/

Evolution of Residual-Strain Distribution through an Overload-Induced Retardation Period during Fatigue Crack Growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S. Y.; Sun, Yinan; An, Ke

2010-01-01

Neutron diffraction was employed to investigate the crack-growth retardation phenomenon after a single tensile overload by mapping both one-dimensional and two-dimensional residual-strain distributions around the crack tip in a series of compact-tension specimens representing various crack-growth stages through an overload-induced retardation period. The results clearly show a large compressive residual-strain field near the crack tip immediately after the overload. As the fatigue crack propagates through the overload-induced plastic zone, the compressive residual strains are gradually relaxed, and a new compressive residual-strain field is developed around the propagating crack tip, illustrating that the subsequent fatigue-induced plastic zone grows out of themore » large plastic zone caused by the overloading. The relationship between the overload-induced plastic zone and subsequent fatigue-induced plastic zone, and its influence on the residual-strain distributions in the perturbed plastic zone are discussed.« less

A new global plate velocity model using space geodetic data, REVEL

NASA Astrophysics Data System (ADS)

Sella, G. F.; Dixon, T. H.; Mao, A.; Stein, S.

2001-12-01

Our model describes the relative velocities of 19 plates and continental blocks, and is derived from publicly available space geodetic (primarily GPS) data for the period 1993-2000. We include an independent and rigorous estimate for GPS velocity uncertainties in order to assess plate rigidity, and propagate these uncertainties to the velocity predictions. By excluding sites that may be influenced by seismic cycle effects within the plate boundary zone as well sites affected by glacial isostatic adjustment, we believe the plate velocity model is representative of geologically Recent motions (last ~10,000 years) and have termed it REVEL, for Recent velocity. Departures from short term rigid plate behaviour due to glacial isostatic adjustment are clearly observed for North America and Eurasia. Australia shows possible differences from rigid plate behavior in a manner consistent with its mapped intraplate stress field. We see statistically significant differences between the velocity predictions of REVEL-2000 and those of the NUVEL-1A geologic model for about one third of tested plate pairs. Pacific-North America motion and motion of the Caribbean plate with respect to North and South America are significantly faster than NUVEL-1A, presumably reflecting systematic errors in the geological model because the relevant rate data do not reflect the full plate rate. Many other differences between the geodetic and geological models appear to reflect real velocity changes over the last few million years. Nubia-Arabia and Arabia-Eurasia appear to be slowing, perhaps related to the collision of Arabia with Eurasia and consequent increased resistance to Arabia's northward motion Several other plate pairs, including Nazca-Pacific, Nazca-South America and Nubia-South America, are experiencing gradual slowing that dates back to about 25 Ma. This is the time of the initiation of the modern Andes mountains, and we speculate that associated crustal thickening on the leading edge of South America may play a role in this deceleration by affecting the balance of plate driving forces.

High-velocity frictional properties of Alpine Fault rocks: Mechanical data, microstructural analysis, and implications for rupture propagation

NASA Astrophysics Data System (ADS)

Boulton, Carolyn; Yao, Lu; Faulkner, Daniel R.; Townend, John; Toy, Virginia G.; Sutherland, Rupert; Ma, Shengli; Shimamoto, Toshihiko

2017-04-01

The Alpine Fault in New Zealand is a major plate-bounding structure that typically slips in ∼M8 earthquakes every c. 330 years. To investigate the near-surface, high-velocity frictional behavior of surface- and borehole-derived Alpine Fault gouges and cataclasites, twenty-one rotary shear experiments were conducted at 1 MPa normal stress and 1 m/s equivalent slip velocity under both room-dry and water-saturated (wet) conditions. In the room-dry experiments, the peak friction coefficient (μp = τp/σn) of Alpine Fault cataclasites and fault gouges was consistently high (mean μp = 0.67 ± 0.07). In the wet experiments, the fault gouge peak friction coefficients were lower (mean μp = 0.20 ± 0.12) than the cataclasite peak friction coefficients (mean μp = 0.64 ± 0.04). All fault rocks exhibited very low steady-state friction coefficients (μss) (room-dry experiments mean μss = 0.16 ± 0.05; wet experiments mean μss = 0.09 ± 0.04). Of all the experiments performed, six experiments conducted on wet smectite-bearing principal slip zone (PSZ) fault gouges yielded the lowest peak friction coefficients (μp = 0.10-0.20), the lowest steady-state friction coefficients (μss = 0.03-0.09), and, commonly, the lowest specific fracture energy values (EG = 0.01-0.69 MJ/m2). Microstructures produced during room-dry and wet experiments on a smectite-bearing PSZ fault gouge were compared with microstructures in the same material recovered from the Deep Fault Drilling Project (DFDP-1) drill cores. The near-absence of localized shear bands with a strong crystallographic preferred orientation in the natural samples most resembles microstructures formed during wet experiments. Mechanical data and microstructural observations suggest that Alpine Fault ruptures propagate preferentially through water-saturated smectite-bearing fault gouges that exhibit low peak and steady-state friction coefficients.

Frictional properties of DFDP-1 Alpine Fault rocks under hydrothermal conditions and high shear strain

NASA Astrophysics Data System (ADS)

Niemeijer, André R.; Boulton, Carolyn; Toy, Virginia; Townend, John; Sutherland, Rupert

2015-04-01

The Alpine Fault, New Zealand, is a major plate-bounding fault that accommodates 65-75% of the total relative motion between the Australian and Pacific plates. Paleoseismic evidence of large-displacement surface-rupturing events, as well as an absence of measurable contemporary surface deformation, indicates that the fault slips mostly in quasi-periodic large-magnitude earthquakes (< Mw 8.0). To understand the mechanics of earthquakes, it is important to study the evolution of frictional properties of the fault rocks under conditions representative of the potential hypocentral depth. Here, we present data obtained on drill core samples of rocks that surround the principal slip zone(s) (PSZ) of the Alpine Fault and the PSZ itself. The drill core samples were obtained during phase 1 of the Deep Fault Drilling Project (DFDP-1) in 2011 at relatively shallow depths (down to ~150 m). Simulated fault gouges were sheared under elevated pressure and temperature conditions in a hydrothermal ring shear apparatus. We performed experiments at temperatures of 25, 150, 300, 450 ° C, and 600 oC. Using the shallow geothermal gradient of 63 ° C/km determined in DFDP-1, our highest temperature corresponds to a depth of ~7 km (Sutherland et al. 2012); it would correspond to 10 km depth using a more moderate geotherm of 45 oC/km (Toy et al. 2010). All samples show a transition from velocity-strengthening behavior, i.e. a positive value of (a-b), to velocity-weakening behavior, i.e. a negative value of (a-b) at a temperature of 150 ° C. The transition depends on the absolute value of sliding velocity, with velocity-weakening dominating at lower sliding velocities. At 600 oC, velocity-strengthening dominates at low sliding velocity, whereas the high-velocity steps are all velocity-weakening. Moreover, shear stress depends linearly on effective normal stress at 600 oC, indicating that shearing is essentially frictional and that no transition to ductile (normal stress independent) flow has occurred. Thus, depending on the background (nucleation) strain rate, our data indicate that the Alpine Fault should be able to generate earthquakes at all temperatures above room temperature. However, at the highest temperature investigated (600 oC), the transition to velocity-weakening is postponed to slip rates above 10 mm/s (strain rate ~10-2 s-1). This observation, combined with the absence of strength recovery after long holds, suggests that seismic slip may propagate into regions of the fault unlikely to nucleate earthquakes. We propose that in our porous gouges, thermally activated processes operate simultaneously with granular flow, postponing ductile flow to higher temperatures or lower strain rates. Sutherland, R., V.G. Toy, J. Townend, S.C. Cox, J.D. Eccles, D.R. Faulkner, D.J. Prior, R.J.Norris, E. Mariani, C. Boulton, B.M. Carpenter, C.D. Menzies, T.A. Little, M. Hasting, G.De Pascale, R.M. Langridge, H.R. Scott, Z. Reid-Lindroos, B. Fleming (2012), Drilling reveals fluid control on architecture and rupture of the Alpine Fault, New Zealand, Geology,40, 1143-1146, doi:10.1130/G33614.1. Toy, V.G., Craw, D., Cooper, A.F., and R.J. Norris (2010), Thermal regime in the central Alpine Fault zone, New Zealand: Constraints from microstructures, biotite chemistry and fluid inclusion data, Tectonophysics, doi:10.1016/j.tecto.2009.12.013

The dependence of Ammonium-Nitrate Fuel-Oil (ANFO) detonation on confinement

DOE PAGES

Jackson, Scott I.

2016-11-17

As detonation is a coupled fluid-chemical process, flow divergence inside the detonation reaction zone can strongly influence detonation velocity and energy release. Such divergence is responsible for the diameter-effect and failure-diameter phenomena in condensed-phase explosives and particularly dominant in detonation of nonideal explosives such as Ammonium Nitrate and Fuel Oil (ANFO). In this study, the effect of reaction zone flow divergence on ANFO detonation was explored through variation of the inert confinement and explosive diameter in the rate-stick geometry with cylinder expansion experiments. New tests are discussed and compared to prior experiments. Presented results include the detonation velocity as amore » function of diameter and confinement, reaction zone times, detonation product isentropes and energies, as well as sonic surface pressures and velocities. Product energy densities and isentropes were found to increase with detonation velocity, indicating more complete chemical reaction with increased detonation velocity. In addition, detonation reaction zone times were found to scale with the acoustic transit time of the confiner wall and used to show that the ANFO diameter effect scaled with the reaction zone time for a particle along the flow centerline, regardless of the confinement. Such a result indicates that the ANFO reaction mechanisms are sufficiently slow that the centerline fluid expansion timescale is a limiting factor controlling detonation velocity and energy release.« less

Ionization Waves of Arbitrary Velocity

NASA Astrophysics Data System (ADS)

Turnbull, D.; Franke, P.; Katz, J.; Palastro, J. P.; Begishev, I. A.; Boni, R.; Bromage, J.; Milder, A. L.; Shaw, J. L.; Froula, D. H.

2018-06-01

Flying focus is a technique that uses a chirped laser beam focused by a highly chromatic lens to produce an extended focal region within which the peak laser intensity can propagate at any velocity. When that intensity is high enough to ionize a background gas, an ionization wave will track the intensity isosurface corresponding to the ionization threshold. We report on the demonstration of such ionization waves of arbitrary velocity. Subluminal and superluminal ionization fronts were produced that propagated both forward and backward relative to the ionizing laser. All backward and all superluminal cases mitigated the issue of ionization-induced refraction that typically inhibits the formation of long, contiguous plasma channels.

An evaluation of the use of new Doppler methods for detecting longitudinal function abnormalities in a pacing-induced heart failure model

NASA Technical Reports Server (NTRS)

Tabata, Tomotsugu; Cardon, Lisa A.; Armstrong, Guy P.; Fukamach, Kiyotaka; Takagaki, Masami; Ochiai, Yoshie; McCarthy, Patrick M.; Thomas, James D.

2003-01-01

BACKGROUND: Doppler tissue echocardiography and color M-mode Doppler flow propagation velocity have proven useful in evaluating cross-sections of patients with left ventricular (LV) dysfunction, but experience with serial changes is limited. Purpose and methods: We tested their use by evaluating the temporal changes of LV function in a pacing-induced congestive heart failure model. Rapid ventricular pacing was initiated and maintained in 20 dogs for 4 weeks. Echocardiography was performed at baseline and weekly during brief pacing cessation. RESULTS: With rapid pacing, LV volume significantly increased and ejection fraction (57%-28%), stroke volume (37-18 mL), and mitral annulus systolic velocity (16.1-6.6 cm/s) by Doppler tissue echocardiography significantly decreased, with ejection fraction and mitral annulus systolic velocity closely correlated (r = 0.706, P <.0001). In contrast to the mitral inflow velocities, mitral annulus early diastolic velocity decreased steadily (12.3-7.3 cm/s) resulting in a dramatic decrease in mitral annulus early/late (1.22-0.57) diastolic velocity with no tendency toward pseudonormalization. The color M-mode Doppler flow propagation velocity also showed significant steady decrease (57-24 cm/s) throughout the pacing period. Multiple regression analysis chose mitral annulus systolic velocity (r = 0.895, P <.0001) and propagation velocity (r = 0.782, P <.0001) for the most important factor predicting LV systolic and diastolic function, respectively. CONCLUSIONS: Doppler tissue echocardiography and color M-mode Doppler flow could evaluate the serial deterioration in LV dysfunction throughout the pacing period. These were more useful in quantifying progressive LV dysfunction than conventional ehocardiographic techniques, and were probably relatively independent of preload. These techniques could be suitable for longitudinal evaluation in addition to the cross-sectional study.

Influence of off-great-circle propagation of Rayleigh waves on event-based surface wave tomography in Northeast China

NASA Astrophysics Data System (ADS)

Chen, Haopeng; Ni, Sidao; Chu, Risheng; Chong, Jiajun; Liu, Zhikun; Zhu, Liangbao

2018-05-01

Surface waves are generally assumed to propagate along great-circle paths in most surface-wave tomography. However, when lateral heterogeneity is strong, off-great-circle propagation may occur and deteriorate surface wave tomography results based on the great-circle assumption. In this study, we used teleseismic waveforms recorded by the NECESSArray in Northeast China to study off-great-circle propagation of Rayleigh waves using the beamforming method and evaluated the influence of off-great-circle propagation on event-based surface wave tomography. The results show that arrival angle anomalies generally increase with decreasing period. The arrival angle anomalies at 60 and 50 s periods are smaller than that at 40 and 30 s periods, which indicates that the off-great-circle propagation is relatively weak for longer periods. At 30 s period, the arrival angle anomalies are relatively larger and some of the measurements can exceed 20°, which represents a strong off-great-circle propagation effect. In some areas, the arrival angle anomalies of adjacent events differ significantly, which may be attributed to multipathing propagation of surface waves. To evaluate the influence of off-great-circle propagation on event-based surface wave tomography, we used measured arrival angle anomalies to correct two-station phase velocity measurements, and performed azimuthal anisotropy tomography using dispersion datasets with and without the arrival angle correction. At longer periods, such as 60 s, the influence of off-great-circle propagation on surface wave tomography is weak even though the corrected model has better data fit than the uncorrected model. However, the influence of off-great-circle propagation is non-negligible at short periods. The tomography results at 30 s period show that the differences in phase velocity, the strength of anisotropy and the fast direction can be as large as 1.5 per cent, 1.0 per cent and 30°, respectively. Furthermore, the corrected phase velocity is systematically lower than that without correction. This study illustrates the necessity of studying the off-great-circle propagation of surface waves to improve the accuracy of event-based surface wave tomography, especially for shorter periods.

Volcanic avalanche fault zone with pseudotachylite and gouge in French Massif Central

NASA Astrophysics Data System (ADS)

Bernard, Karine; van Wyk de Vries, Benjamin

2017-11-01

Structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non-depositional to depositional conditions during volcanic avalanche emplacement. In the well-exposed impact-sheared contact along volcanic avalanche fault zone in the French Massif Central, we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress. Sequential events of basal aggradation along avalanche fault zone have been established related to fractal D-values, temperature pressure regime and oscillatory stress during slow wave velocity. A typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge. A cataclastic gradient is characterised by the fractal D-values from 2.7 in jigsaw breccias with pseudotachylite partial melt, to 2.6 in the polymodal gouge. Shock, brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris-avalanche deposit. Gouge microstructures show granular segregation, cataclasis with antithetic rotational Riedel shear, and an arching effect between the Riedel shear bands. X-ray microtomography provided 3D microfabrics along the clastic vein in the sandy-gouge. From the available statistical dataset, a few equations have been developed implicating the same cataclastic origin with a co-genetic evolution of lithofacies. An impact wave during primary shear propagation may contribute to produce hydroclastic matrix, pseudotachylite partial melt and proximal gouge thixotropy with v 50m/s and a T < 654 °C. The interseismic period with oscillatory stress is related to crushed clasts and basaltic melt around 800 °C, Riedel shear bands with granular segregation along the fault gouge. The secondary shock by matrix-rich avalanche (ΔP = 10GPa, T ≥ 1000-1500 °C) contributes to quartz microstructures along the avalanche basal contact and quartz spheroids in microscopic cataclastic shear bands. Decompression around 654-800 °C is related to tertiary sub-vertical oscillations with a backward moving shock and antithetic rotational fault megablock. Semi-quantitative analyses of seismogenic fault basement contribute to establish the localised conditions related to sequential aggradation along volcanic avalanche fault zone.

Dynamic fracture network around faults: implications for earthquake ruptures, ground motion and energy budget

NASA Astrophysics Data System (ADS)

Okubo, K.; Bhat, H. S.; Rougier, E.; Lei, Z.; Knight, E. E.; Klinger, Y.

2017-12-01

Numerous studies have suggested that spontaneous earthquake ruptures can dynamically induce failure in secondary fracture network, regarded as damage zone around faults. The feedbacks of such fracture network play a crucial role in earthquake rupture, its radiated wave field and the total energy budget. A novel numerical modeling tool based on the combined finite-discrete element method (FDEM), which accounts for the main rupture propagation and nucleation/propagation of secondary cracks, was used to quantify the evolution of the fracture network and evaluate its effects on the main rupture and its associated radiation. The simulations were performed with the FDEM-based software tool, Hybrid Optimization Software Suite (HOSSedu) developed by Los Alamos National Laboratory. We first modeled an earthquake rupture on a planar strike-slip fault surrounded by a brittle medium where secondary cracks can be nucleated/activated by the earthquake rupture. We show that the secondary cracks are dynamically generated dominantly on the extensional side of the fault, mainly behind the rupture front, and it forms an intricate network of fractures in the damage zone. The rupture velocity thereby significantly decreases, by 10 to 20 percent, while the supershear transition length increases in comparison to the one with purely elastic medium. It is also observed that the high-frequency component (10 to 100 Hz) of the near-field ground acceleration is enhanced by the dynamically activated fracture network, consistent with field observations. We then conducted the case study in depth with various sets of initial stress state, and friction properties, to investigate the evolution of damage zone. We show that the width of damage zone decreases in depth, forming "flower-like" structure as the characteristic slip distance in linear slip-weakening law, or the fracture energy on the fault, is kept constant with depth. Finally, we compared the fracture energy on the fault to the energy absorbed by the secondary fracture network to better understand the earthquake energy budget. We conclude that the secondary fracture network plays an important role on the dynamic earthquake rupture, its radiated wave field and the overall energy budget.

Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves

USGS Publications Warehouse

Ellsworth, William L.; Malin, Peter E.

2011-01-01

Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by Fg, can propagate. Here we show with core samples, well logs and Fg-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (FL) and Rayleigh-type- (FR) guided waves, but also a new fault-guided wave, which we name FF. As recorded 2.7 km underground, FF is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that FF travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, FF at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site.

Backward propagating branch of surface waves in a semi-bounded streaming plasma system

NASA Astrophysics Data System (ADS)

Lim, Young Kyung; Lee, Myoung-Jae; Seo, Ki Wan; Jung, Young-Dae

2017-06-01

The influence of wake and magnetic field on the surface ion-cyclotron wave is kinetically investigated in a semi-bounded streaming dusty magnetoplasma in the presence of the ion wake-field. The analytic expressions of the frequency and the group velocity are derived by the plasma dielectric function with the spectral reflection condition. The result shows that the ion wake-field enhances the wave frequency and the group velocity of the surface ion-cyclotron wave in a semi-bounded dusty plasma. It is found that the frequency and the group velocity of the surface electrostatic-ion-cyclotron wave increase with an increase of the strength of the magnetic field. It is interesting to find out that the group velocity without the ion flow has the backward propagation mode in a semi-bounded dusty plasma. The variations due to the frequency and the group velocity of the surface ion-cyclotron wave are also discussed.

Evaluation of factors that influence estimated zones of transport for six municipal wells in Clark County, Washington

USGS Publications Warehouse

Orzol, L.L.; Truini, Margot

1999-01-01

Sensitivity of the zones of transport to change in the discharge rate of the selected well, porosity, and hydraulic conductivity, as well as to the presence or absence of interfering wells, was evaluated at six well sites to evaluate the effect of uncertainties in these factors on the size and shape of zones of transport. Uncertainty in porosity contributed the most to the uncertainty in delineating the zones of transport. Uncertainty in other factors, such as well discharge rate and horizontal hydraulic conductivity, had measurable effects on the zones of transport, but errors introduced through these factors were less significant. Insight into the causes of the changes in the size and shape of the zones of transport to varying conditions was gained by evaluating the simulated water budget and ground-water levels in the vicinity of the well. Changes in the simulated water budget and ground-water levels provided information to better understand the effects of uncertainties in the data on simulation results.The results of this study suggest that ground-water velocity is the underlying control on the size of the zones of transport. The regional hydraulic gradient is the most significant factor controlling the shape and orientation of the zones of transport. Spatial variation in recharge, discharge, and hydraulic properties can also affect the shape of the zones of transport, however. Underestimation of porosity or overestimation of horizontal hydraulic conductivity leads to overestimation of ground-water velocity and overestimation of the size of zones of transport. Overestimation of porosity or underestimation of horizontal hydraulic conductivity leads to underestimation of ground-water velocity and underestimation of the size of zones of transport. Well discharge rate affects ground-water velocities near the well. Underestimation of discharge (and therefore velocities) will result in underestimation of the size of the zones of transport. The sensitivity of estimated zones of transport to uncertainty in parameters such as porosity and horizontal hydraulic conductivity is a function of the well discharge rate and the proximity of the well to boundaries, such as streams and rivers.

Kinematics, partitioning and the relationship between velocity and strain in shear zones

NASA Astrophysics Data System (ADS)

Murphy, Justin James

Granite Point, southeast Washington State, captures older distributed deformation deflected by younger localized deformation. This history agrees with mathematical modeling completed by Watkinson and Patton (2005; 2007 in prep). This model suggests that distributed strain occurs at a lower energy threshold than localized strain and predicts deformation histories similar to Granite Point. Ductile shear zones at Granite Point define a zone of deformation where strain is partitioned and localized into at least ten sub parallel shear zones with sinistral, west side down shear sense. Can the relative movement of the boundaries of this partitioned system be reconstructed? Can partitioning be resolved from a distributed style of deformation? The state of strain and kinematics of actively deforming zones was studied by relating the velocity field to strain. The Aleutian Arc, Alaska and central Walker Lane, Nevada were chosen because they have a wealth of geologic data and are recognized examples of obliquely deforming zones. The graphical construction developed by Declan De Paor is ideally suited for this application because it provides a spatially referenced visualization of the relationship between velocity and strain. The construction of De Paor reproduces the observed orientation of strain in the Aleutian Arc, however, the spatial distribution of GPS stations suggest a component of partitioning. Partitioning does not provide a unique solution and cannot be differentiated from a combination of partitioning and distributed strain. In the central Walker Lane, strain trajectories can be reproduced at the domain scale. Furthermore, the effect of anisotropy from Paleozoic through Cenozoic crustal structure, which breaks the regional strain field into pure shear and simple shear dominated transtension can be detected. Without GPS velocities to document strictly coaxial strain, the strain orientation should not be taken as the velocity orientation. The strain recorded at Granite Point should not be used to reconstruct the relative movement of the boundaries because the strain direction may not be parallel to the velocity orientation. Kinematic reconstructions of obliquely deforming zones that assume a palaeo-velocity orientation equal to the measured orientation of finite strain may not accurately reflect the deviation between velocity and strain.

Characteristics of shocks in the solar corona, as inferred from radio, optical, and theoretical investigations

NASA Technical Reports Server (NTRS)

Maxwell, A.; Dryer, M.

1982-01-01

Solar radio bursts of spectral type II provide one of the chief diagnostics for the propagation of shocks through the solar corona. Radio data on the shocks are compared with computer models for propagation of fast-mode MHD shocks through the solar corona. Data on coronal shocks and high-velocity ejecta from solar flares are then discussed in terms of a general model consisting of three main velocity regimes.

Explosion source strong ground motions in the Mississippi embayment

USGS Publications Warehouse

Langston, C.A.; Bodin, P.; Powell, C.; Withers, M.; Horton, S.; Mooney, W.

2006-01-01

Two strong-motion arrays were deployed for the October 2002 Embayment Seismic Excitation Experiment to study the spatial variation of strong ground motions in the deep, unconsolidated sediments of the Mississippi embayment because there are no comparable strong-motion data from natural earthquakes in the area. Each linear array consisted of eight three-component K2 accelerographs spaced 15 m apart situated 1.2 and 2.5 kin from 2268-kg and 1134-kg borehole explosion sources, respectively. The array data show distinct body-wave and surface-wave arrivals that propagate within the thick, unconsolidated sedimentary column, the high-velocity basement rocks, and small-scale structure near the surface. Time-domain coherence of body-wave and surface-wave arrivals is computed for acceleration, velocity, and displacement time windows. Coherence is high for relatively low-frequency verticalcomponent Rayleigh waves and high-frequency P waves propagating across the array. Prominent high-frequency PS conversions seen on radial components, a proxy for the direct S wave from earthquake sources, lose coherence quickly over the 105-m length of the array. Transverse component signals are least coherent for any ground motion and appear to be highly scattered. Horizontal phase velocity is computed by using the ratio of particle velocity to estimates of the strain based on a plane-wave-propagation model. The resulting time-dependent phase-velocity map is a useful way to infer the propagation mechanisms of individual seismic phases and time windows of three-component waveforms. Displacement gradient analysis is a complementary technique for processing general spatial-array data to obtain horizontal slowness information.

A device for emulating cuff recordings of action potentials propagating along peripheral nerves.

PubMed

Rieger, Robert; Schuettler, Martin; Chuang, Sheng-Chih

2014-09-01

This paper describes a device that emulates propagation of action potentials along a peripheral nerve, suitable for reproducible testing of bio-potential recording systems using nerve cuff electrodes. The system is a microcontroller-based stand-alone instrument which uses established nerve and electrode models to represent neural activity of real nerves recorded with a nerve cuff interface, taking into consideration electrode impedance, voltages picked up by the electrodes, and action potential propagation characteristics. The system emulates different scenarios including compound action potentials with selectable propagation velocities and naturally occurring nerve traffic from different velocity fiber populations. Measured results from a prototype implementation are reported and compared with in vitro recordings from Xenopus Laevis frog sciatic nerve, demonstrating that the electrophysiological setting is represented to a satisfactory degree, useful for the development, optimization and characterization of future recording systems.

Attenuation characteristics of the fundamental modes that propagate in buried iron water pipes.

PubMed

Long, R; Lowe, M; Cawley, P

2003-09-01

The attenuation of the fundamental non-torsional modes that propagate down buried iron water pipes has been studied. The mode shapes, mode attenuation due to leakage into the surrounding medium and the scattering of the modes as they interact with pipe joints and fittings have been investigated. In the low frequency region the mode predicted to dominate over significant propagation distances approximates a plane wave in the water within the pipe. The established acoustic technique used to locate leaks in buried iron water pipes assumes that leak noise propagates as a single non-dispersive mode at a velocity related to the low frequency asymptote of this water borne mode. Experiments have been conducted on buried water mains at test sites in the UK to verify the attenuation and velocity dispersion predictions.

Criticality in third order lovelock gravity and butterfly effect

NASA Astrophysics Data System (ADS)

Qaemmaqami, Mohammad M.

2018-01-01

We study third order Lovelock Gravity in D=7 at the critical point which three (A)dS vacua degenerate into one. We see there is not propagating graviton at the critical point. And also we compute the butterfly velocity for this theory at the critical point by considering the shock wave solutions near horizon, this is important to note that although there is no propagating graviton at the critical point, due to boundary gravitons the butterfly velocity is non-zero. Finally we observe that the butterfly velocity for third order Lovelock Gravity at the critical point in D=7 is less than the butterfly velocity for Einstein-Gauss-Bonnet Gravity at the critical point in D=7 which is less than the butterfly velocity in D = 7 for Einstein Gravity, vB^{E.H}>vB^{E.G.B}>vB^{3rd Lovelock} . Maybe we can conclude that by adding higher order curvature corrections to Einstein Gravity the butterfly velocity decreases.

Detailed crustal structure in the area of the southern Apennines-Calabrian Arc border from local earthquake tomography

NASA Astrophysics Data System (ADS)

Totaro, C.; Koulakov, I.; Orecchio, B.; Presti, D.

2014-12-01

We present a new seismic velocity model for the southern Apennines-Calabrian Arc border region with the aim to better define the crustal structures at the northern edge of the Ionian subduction zone. This sector also includes the Pollino Mts. area, where a seismic sequence of thousands of small to moderate earthquakes has been recorded between spring 2010 and 2013. In this sector a seismic gap was previously hypothesized by paleoseismological evidences associated with the lack of major earthquakes in historical catalogs. To perform the tomographic inversion we selected ca. 3600 earthquakes that have occurred in the last thirty years and recorded by permanent and temporary networks managed by INGV and Calabria University. Using for the first time the Local Tomography Software for passive tomography inversion (LOTOS hereinafter) to crustal analysis in southern Italy, we have computed the distribution of Vp, Vs, and the Vp/Vs ratio. The obtained velocity model, jointly evaluated with results of synthetic modeling, as well as with the hypocenter distribution and geological information, gives us new constraints on the geodynamical and structural knowledge of the study area. The comparison between the shallow tomography sections and surface geology shows good correlation between velocity patterns and the main geological features of the study area. In the upper crust a low-velocity anomaly of P- and S-waves is detectable beneath the Pollino Mts. area and seems to separate the Calabrian and southern Apennines domains, characterized by higher velocities. The distributions of high Vp/Vs ratio, representing strongly fractured rocks with likely high fluid content, clearly correlate with areas of significant seismicity. In the lower crust we detect a clear transition from high to low seismic velocities in correspondence with the Tyrrhenian coast of the study area, which may represent the transition from the thinner Tyrrhenian crust to the thicker one beneath Calabria. In this area, also characterized by a progressive detachment of a retreating lithospheric slab, the generation of a Subduction-Transform Edge Propagator (STEP) fault zone, that laterally decouples subducting lithosphere from non-subducting lithosphere in a scissor type of fashion, may have taken place. These conditions imply the existence of a kinematic decoupling which allows for differential movement between the Calabrian Arc and the southern Apennine chain. The low velocity anomaly separating the southern Apennines and the Calabrian Arc domain may be related to fluid upwelling occurring in correspondence with the northern edge of the Calabrian subducting slab.

Spatio-temporal Evolution of On-going Tokai Slow Thrust Slip Event, Central Japan

NASA Astrophysics Data System (ADS)

Miyazaki, S.; Segall, P.; Kato, T.; McGuire, J.; Hatanaka, Y.

2003-12-01

We investigate an on-going slow thrust slip event that occurred at a subduction zone along the Nankai Trough off central Japan. The area we investimate, referred as the Tokai seismic gap, is located to the east of the 1944 Tonankai earthquake, which did not slip in the 1944 event. Continuous GPS data from April 1996 to the end of 1999 shows that the stations in this region have secular velocities of ˜ 2 cm/yr to the northwest relative to the landward plate. The GPS time series show an abrupt increase in rate in late June, 2000. The accelerated rate is currently on-going. We model this non-secular deformation, which we refer to the 2000 Tokai slow slip event, by transient slip at the plate interface and estimate their distribution with Kalman Filter based inversion methods. This event initiated around (137.3oE, 34.9oN) almost at the same time of the onset of volcanic activity on Miyake-jima in late June, 2000. This suggests that the 2000 Tokai slow slip event is triggered by the volcanic activity on Miyake-jima. Then the locus of the slip propagated to (137.5oE, 34.75oN) in second half of 2000, and kept slipping at the maximum rate of ˜ 15cm/yr through 2001. The peak slip-rate propagated to around (137.75oE, 34.9oN) in early 2002. The depth of slip zone is ˜ 25km, which may correspond to the lower edge of the seismogenic zone for the anticipated Tokai earthquake defined from seismicity. The cumulative moment magnitude of the slow slip event to date is MW ˜ 6.8. The duration of this event is longer than previously studied slow slip events using GPS data, including the 1996 Bungo slow slip event (about 1 year) and the 1996 and the 2000 Boso slow events (a few weeks).

Kilometer-Spaced GNSS Array for Ionospheric Irregularity Monitoring

NASA Astrophysics Data System (ADS)

Su, Yang

This dissertation presents automated, systematic data collection, processing, and analysis methods for studying the spatial-temporal properties of Global Navigation Satellite Systems (GNSS) scintillations produced by ionospheric irregularities at high latitudes using a closely spaced multi-receiver array deployed in the northern auroral zone. The main contributions include 1) automated scintillation monitoring, 2) estimation of drift and anisotropy of the irregularities, 3) error analysis of the drift estimates, and 4) multi-instrument study of the ionosphere. A radio wave propagating through the ionosphere, consisting of ionized plasma, may suffer from rapid signal amplitude and/or phase fluctuations known as scintillation. Caused by non-uniform structures in the ionosphere, intense scintillation can lead to GNSS navigation and high-frequency (HF) communication failures. With specialized GNSS receivers, scintillation can be studied to better understand the structure and dynamics of the ionospheric irregularities, which can be parameterized by altitude, drift motion, anisotropy of the shape, horizontal spatial extent and their time evolution. To study the structuring and motion of ionospheric irregularities at the sub-kilometer scale sizes that produce L-band scintillations, a closely-spaced GNSS array has been established in the auroral zone at Poker Flat Research Range, Alaska to investigate high latitude scintillation and irregularities. Routinely collecting low-rate scintillation statistics, the array database also provides 100 Hz power and phase data for each channel at L1/L2C frequency. In this work, a survey of seasonal and hourly dependence of L1 scintillation events over the course of a year is discussed. To efficiently and systematically study scintillation events, an automated low-rate scintillation detection routine is established and performed for each day by screening the phase scintillation index. The spaced-receiver technique is applied to cross-correlated phase and power measurements from GNSS receivers. Results of horizontal drift velocities and anisotropy ellipses derived from the parameters are shown for several detected events. Results show the possibility of routinely quantifying ionospheric irregularities by drifts and anisotropy. Error analysis on estimated properties is performed to further evaluate the estimation quality. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts. A case study of a single scintillating satellite observed by the array is used to demonstrate the uncertainty estimation process. The distributed array is used in coordination with other measuring techniques such as incoherent scatter radar and optical all-sky imagers. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30-minute period are made and compared to a collocated incoherent scatter radar, and show good agreement in horizontal drift speed and direction during periods of scintillation for cases when the characteristic velocity is less than the drift velocity. The methods demonstrated are extensible to other zones and other GNSS arrays of varying size, number, ground distribution, and transmitter frequency.

Lesion contrast and detection using sonoelastographic shear velocity imaging: preliminary results

NASA Astrophysics Data System (ADS)

Hoyt, Kenneth; Parker, Kevin J.

2007-03-01

This paper assesses lesion contrast and detection using sonoelastographic shear velocity imaging. Shear wave interference patterns, termed crawling waves, for a two phase medium were simulated assuming plane wave conditions. Shear velocity estimates were computed using a spatial autocorrelation algorithm that operates in the direction of shear wave propagation for a given kernel size. Contrast was determined by analyzing shear velocity estimate transition between mediums. Experimental results were obtained using heterogeneous phantoms with spherical inclusions (5 or 10 mm in diameter) characterized by elevated shear velocities. Two vibration sources were applied to opposing phantom edges and scanned (orthogonal to shear wave propagation) with an ultrasound scanner equipped for sonoelastography. Demodulated data was saved and transferred to an external computer for processing shear velocity images. Simulation results demonstrate shear velocity transition between contrasting mediums is governed by both estimator kernel size and source vibration frequency. Experimental results from phantoms further indicates that decreasing estimator kernel size produces corresponding decrease in shear velocity estimate transition between background and inclusion material albeit with an increase in estimator noise. Overall, results demonstrate the ability to generate high contrast shear velocity images using sonoelastographic techniques and detect millimeter-sized lesions.

Low frequency wave propagation in a cold magnetized dusty plasma

NASA Astrophysics Data System (ADS)

Sarkar, S.; Ghosh, S.; Khan, M.

1998-12-01

In this paper several characteristics of low frequency waves in a cold magnetized dusty plasma propagating parallel and perpendicular to the static background magnetic field have been investigated. In the case of parallel propagation the negatively charged dust particles resonate with the right circularly polarized (RCP) component of em waves when the wave frequency equals the dust cyclotron frequency. It has been shown that an RCP wave in dusty plasma consists of two branches and there exists a region where an RCP wave propagation is not possible. Dispersion relation, phase velocity and group velocity of RCP waves have been obtained and propagation characteristics have been shown graphically. Poynting flux and Faraday rotation angles have been calculated for both lower and upper branches of the RCP wave. It has been observed that sense of rotation of the plane of polarization of the RCP wave corresponding to two distinct branches are opposite. Finally, the effect of dust particles on the induced magnetization from the inverse Faraday effect (IFE) due to the interaction of low frequency propagating and standing em waves with dusty plasmas has been evaluated.

Infrasonic troposphere-ionosphere coupling in Hawaii

NASA Astrophysics Data System (ADS)

Garces, M. A.

2011-12-01

The propagation of infrasonic waves in the ionospheric layers has been considered since the 1960's. It is known that space weather can alter infrasonic propagation below the E layer (~120 km altitude), but it was thought that acoustic attenuation was too severe above this layer to sustain long-range propagation. Although volcanoes, earthquakes and tsunamis (all surface sources) appear to routinely excite perturbations in the ionospheric F layer by the propagation of acoustic and acoustic-gravity waves through the atmosphere, there are few reports of the inverse pathway. This paper discusses some of the routine ground-based infrasonic array observations of ionospheric returns from surface sources. These thermospheric returns generally point back towards the source, with an azimuth deviation that can be corrected using the wind velocity profiles in the mesosphere and lower thermosphere. However, the seismic excitation in the North Pacific by the Tohoku earthquake ensonified the coupled lithosphere-atmosphere-ionosphere waveguide in the 0.01 - 0.1 Hz frequency band, producing anomalous signals observed by infrasound arrays in Hawaii. These infrasonic signals propagated at curiously high velocities, suggesting that some assumptions on ionospheric sound generation and propagation could be revisited.

Fatigue crack layer propagation in silicon-iron

NASA Technical Reports Server (NTRS)

Birol, Y.; Welsch, G.; Chudnovsky, A.

1986-01-01

Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

Understanding exchanges across turbulent/stratified zones interfaces

NASA Astrophysics Data System (ADS)

Le Bars, M.; Ribeiro, A.; Le Gal, P.; Aurnou, J. M.

2013-12-01

In many geophysical and astrophysical situations, a turbulent fluid layer is separated from a stably stratified one by a relatively sharp but deformable interface. Examples include the convective and radiative zones in stars, the atmospheric convective layer and overlying stratosphere, the Earth's outer core... While motions in the stratified layer are often neglected, it actually supports oscillatory motions called gravito-inertial waves (GIW) excited by Reynolds stresses, entropy fluctuations and interface deformations associated with the turbulence. Besides their direct observation as for instance in asteroseismology, GIW transport energy, carry momentum, break, mix... and are thus essential for accurate models of global climate and solar or core dynamics. Global integrated models including length scales and time scales spanning many orders of magnitude are required to fully address motions in turbulent and stratified zones and to understand the details of the highly non-linear couplings between rotation, meridional circulation, turbulence and waves: this is clearly very challenging from both analytical and numerical points of view. Here, we present results from two complementary laboratory experiments using water as a working fluid and salt or temperature to control the buoyancy effects, allowing to address the whole range of relevant physical issues in simplified models. In the first set-up, we take benefit from the unusual property of water that its density has a maximum value near 4oC to study its convective and oscillatory motions in a tank with a bottom boundary at about 0oC and a hotter upper surface. High precision local measurements of temperature fluctuations are performed simultaneously in the convective and stratified zones to produce the corresponding power density spectrum and probability density function. In the second set-up, a turbulent jet generated by injection of water impinges upon the interface between a uniform density layer and a stratified one of salted water. The experiment is performed on a rotating table. Velocity measurements are carried out non-intrusively using Particle Imaging Velocimetry in both regions. Our combined results show that (i) the interface acts as a filter which mostly allows for the passing of low frequency perturbations, while (ii) the further propagation of the excited waves in the stratified zone gives rise to selective wave damping, focusing the transported energy and momentum around given frequencies corresponding to selected propagation angles. We explain those results with a simple analytical model, allowing their extension to natural configurations.

Detailed Tremor Migration Styles in Guerrero, Mexico Imaged with Cross-station Cross-correlations

NASA Astrophysics Data System (ADS)

Peng, Y.; Rubin, A. M.

2015-12-01

Tremor occurred downdip of the area that slipped the most during the 2006 slow slip event (SSE) in Guerrero, Mexico, as opposed to Cascadia, where tremor locations and rupture zones of SSEs largely overlap. Here we obtain high resolution tremor locations by applying cross-station cross-correlations [Armbruster et al., 2014] to seismic data from the Meso-America Subduction Experiment deployment. A few 3-station detectors are adopted to capture detailed deformation styles in the tremor "transient zone" and the downdip "sweet spot" as defined in Frank et al., 2014. Similar to Cascadia, tremor activities in our study region were comprised mostly of short tremor bursts lasting minutes to hours. Many of these bursts show clear migration patterns with propagation velocities of hundreds of km/day, comparable to those in Cascadia. However, the propagation of the main tremor front was often not in a simple unilateral fashion. Before the 2006 SSE, we observe 4 large tremor episodes during which both the transient zone and the sweet spot participated, consistent with previous findings [Frank et al., 2014]. The transient zone usually became active a few days after the sweet spot. We find many along-dip migrations with recurrence intervals of about a half day within a region about 10 km along strike and 35 km along dip in the sweet spot, suggesting possible tidal modulation, after the main front moved beyond this region. These migrations appear not to originate at the main front, in contrast to tremor migrations from a few km to tens of km across observed in Cascadia [Rubin and Armbruster, 2013; Peng et al., 2015; Peng and Rubin, submitted], but possibly similar to Shikoku, Japan [Shelly et al., 2007]. We do not observe obvious half-day periodicity for the migrations farther downdip within the sweet spot. During the SSE, the recurrence interval of tremor episodes decreased significantly in both the transient zone and the sweet spot, with that of the former being much shorter. Within the sweet spot, the number of tremor events and the rupture area of each episode also decreased relative to the large pre-SSE episodes. The updip portion of the sweet spot often became active before the downdip portion, consistent with loading from farther updip where the slow slip was concentrated. In contrast, the pre-SSE episodes generally originated farther downdip.

Seismic Wave Velocity in the Subducted Oceanic Crust from Autocorrelation of Tectonic Tremor Signals

NASA Astrophysics Data System (ADS)

Ducellier, A.; Creager, K.

2017-12-01

Hydration and dehydration of minerals in subduction zones play a key role in the geodynamic processes that generate seismicity and that allow tectonic plates to subduct. Detecting the presence of water in the subducted plate is thus crucial to better understand the seismogenesis and the consequent seismic hazard. A landward dipping, low velocity layer has been detected in most subduction zones. In Cascadia, this low velocity zone is characterized by a low S-wave velocity and a very high Poisson's ratio, which has been interpreted as high pore-fluid pressure in the upper half part of the subducted oceanic crust. Most previous studies were based on seismic reflection imaging, receiver function analysis, or body wave tomography, with seismic sources located far from the low velocity zone. In contrast, the sources of the tectonic tremors generated during Episodic Tremor and Slip (ETS) events are located on the plate boundary. As the sources of the tremors are much closer to the low velocity zone, seismic waves recorded during ETS events should illuminate the area with greater precision. Most methods to detect and locate tectonic tremors and low-frequency earthquakes are based on the cross correlation of seismic signals; either signals at the same station for different events, or the same event at different stations. We use the autocorrelation of the seismic signal recorded by eight arrays of stations, located in the Olympic Peninsula, Washington. Each tremor, assumed to be on the plate boundary, generates a direct wave and reflected and converted waves from both the strong shear-wave velocity contrast in the mid-oceanic crust, and from the Moho of the subducted oceanic crust. The time lag between the arrivals of these different waves at a seismic station corresponds to a peak of amplitude on the autocorrelation signals. Using the time lags observed for different locations of the tremor source, we intend to invert for the seismic wave velocity of the subducted oceanic crust under the arrays. Identifying zones with lower S-wave velocity and a high Poisson's ratio will then help detecting the presence of water in the subducted oceanic crust. Our ultimate goal is contributing to a better understanding of the mechanism of ETS and subduction zone processes.

Quasi-Dynamic Versus Fully-Dynamic Simulations of Slip Accumulation on Faults with Enhanced Dynamic Weakening

NASA Astrophysics Data System (ADS)

Lapusta, N.; Thomas, M.; Noda, H.; Avouac, J.

2012-12-01

Long-term simulations that incorporate both seismic events and aseismic slip are quite important for studies of earthquake physics but challenging computationally. To study long deformation histories, most simulation methods do not incorporate full inertial effects (wave propagation) during simulated earthquakes, using quasi-dynamic approximations instead. Here we compare the results of quasi-dynamic simulations to the fully dynamic ones for a range of problems to determine the applicability of the quasi-dynamic approach. Intuitively, the quasi-dynamic approach should do relatively well in problems where wave-mediated effects are relatively simple but should have substantially different (and hence wrong) response when the wave-mediated stress transfers dominate the character of the seismic events. This is exactly what we observe in our simulations. We consider a 2D model of a rate-and-state fault with a seismogenic (steady-state velocity-weakening) zone surrounded by creeping (steady-state velocity-strengthening) areas. If the seismogenic zone is described by the standard Dieterich-Ruina rate-and-state friction, the resulting earthquake sequences consist of relatively simple crack-like ruptures, and the inclusion of true wave-propagation effects mostly serves to concentrate stress more efficiently at the rupture front. Hence, in such models, rupture speeds and slip rates are significantly (several times) lower in the quasi-dynamic simulations compared to the fully dynamic ones, but the total slip, the crack-like nature of seismic events, and the overall pattern of earthquake sequences is comparable, consistently with prior studies. Such behavior can be classified as qualitatively similar but quantitatively different, and it motivates the popularity of the quasi-dynamic methods in simulations. However, the comparison changes dramatically once we consider a model with enhanced dynamic weakening in the seismogenic zone in the form of flash heating. In this case, the fully dynamic simulations produce seismic ruptures in the form of short-duration slip pulses, where the pulses form due to a combination of enhanced weakening and wave effects. The quasi-dynamic simulations in the same model produce completely different results, with large crack-like ruptures, different total slips, different rupture patterns, and different prestress state before large, model-spanning events. Such qualitative differences between the quasi-dynamic and fully-dynamic simulation should result in any model where inertial effects lead to qualitative differences, such as cases with supershear transition or fault with different materials on the two sides. We will present results on our current work on how the quasi-dynamic and fully dynamic simulations compare for the cases with heterogeneous fault properties.

High resolution wavenumber analysis for investigation of arterial pulse wave propagation

NASA Astrophysics Data System (ADS)

Hasegawa, Hideyuki; Sato, Masakazu; Irie, Takasuke

2016-07-01

The propagation of the pulse wave along the artery is relatively fast (several m/s), and a high-temporal resolution is required to measure pulse wave velocity (PWV) in a regional segment of the artery. High-frame-rate ultrasound enables the measurement of the regional PWV. In analyses of wave propagation phenomena, the direction and propagation speed are generally identified in the frequency-wavenumber space using the two-dimensional Fourier transform. However, the wavelength of the pulse wave is very long (1 m at a propagation velocity of 10 m/s and a temporal frequency of 10 Hz) compared with a typical lateral field of view of 40 mm in ultrasound imaging. Therefore, PWV cannot be identified in the frequency-wavenumber space owing to the low resolution of the two-dimensional Fourier transform. In the present study, PWV was visualized in the wavenumber domain using phases of arterial wall acceleration waveforms measured by high-frame-rate ultrasound.

How Eddies Gain, Retain, and Release Water: A Case Study of a Hokkaido Anticyclone

NASA Astrophysics Data System (ADS)

Prants, S. V.; Budyansky, M. V.; Uleysky, M. Yu.

2018-03-01

A Lagrangian methodology is elaborated to identify the origin of water masses in the Kuroshio-Oyashio frontal zone where waters of the Kuroshio Extension and Oyashio Current and of the Japan and Okhotsk Seas converge. It allows one to track the evolution of mesoscale eddies during the satellite-altimetry era and to document how they gain, retain, and release water masses of different origin. The methodology is applied to study warm-core mesoscale anticyclones propagating along the Japan and Kuril Trenches near the eastern coast of Hokkaido Island that have been observed from 1 January 1993 to 10 December 2016 in an altimetry-based velocity field. The Hokkaido eddy, sampled by profiling floats and a few cruises in 2003 and 2004, is analyzed in detail in order to compare Lagrangian simulation results to observations.

Experimental study of the free surface velocity field in an asymmetrical confluence

NASA Astrophysics Data System (ADS)

Creelle, Stephan; Mignot, Emmanuel; Schindfessel, Laurent; De Mulder, Tom

2017-04-01

The hydrodynamic behavior of open channel confluences is highly complex because of the combination of different processes that interact with each other. To gain further insights in how the velocity uniformization between the upstream channels and the downstream channel is proceeding, experiments are performed in a large scale 90 degree angled concrete confluence flume with a chamfered rectangular cross-section and a width of 0.98m. The dimensions and lay-out of the flume are representative for a prototype scale confluence in e.g. drainage and irrigation systems. In this type of engineered channels with sharp corners the separation zone is very large and thus the velocity difference between the most contracted section and the separation zone is pronounced. With the help of surface particle tracking velocimetry the velocity field is recorded from upstream of the confluence to a significant distance downstream of the confluence. The resulting data allow to analyze the evolution of the incoming flows (with a developed velocity profile) that interact with the stagnation zone and each other, causing a shear layer between the two bulk flows. Close observation of the velocity field near the stagnation zone shows that there are actually two shear layers in the vicinity of the upstream corner. Furthermore, the data reveals that the shear layer observed more downstream between the two incoming flows is actually one of the two shear layers next to the stagnation zone that continues, while the other shear layer ceases to exist. The extensive measurement domain also allows to study the shear layer between the contracted section and the separation zone. The shear layers of the stagnation zone between the incoming flows and the one between the contracted flow and separation zone are localized and parameters such as the maximum gradient, velocity difference and width of the shear layer are calculated. Analysis of these data shows that the shear layer between the incoming flows disappears quite quickly, because of the severe flow contraction that aids the flow uniformization. This is also accelerated because of a flow redistribution process that starts already upstream of the confluence, resulting in a lower than expected velocity difference over the shear layer between the bulk of the incoming flows. In contrast, the shear layer between the contracted section and the separation zone proves to be of a significantly higher order of magnitude, with large turbulent structures appearing that get transported far downstream. In conclusion, the resulting understanding of this analysis of velocity fields with a larger field of view shows that when analyzing confluence hydrodynamics, one should pay ample attention to analyze data far enough up and downstream to assess all the relevant processes.

Plate mode velocities in graphite/epoxy plates

NASA Technical Reports Server (NTRS)

Prosser, W. H.; Gorman, M. R.

1994-01-01

Measurements of the velocities of the extensional and flexural plate modes were made along three directions of propagation in four graphite/epoxy composite plates. The acoustic signals were generated by simulated acoustic emission events (pencil lead breaks or Hsu-Neilson sources) and detected by by broadband ultrasonic transducers. The first arrival of the extensional plate mode, which is nondispersive at low frequencies, was measured at a number of different distances from the source along the propagation direction of interest. The velocity was determined by plotting the distance versus arrival time and computing its slope. Because of the large dispersion of the flexural mode, a Fourier phase velocity technique was used to characterize this mode. The velocity was measured up to a frequency of 160 kHz. Theoretical predictions of the velocities of these modes were also made and compared with experimental observations. Classical plate theory yields good agreement with the measured extensional velocities. For predictions of the dispersion of the flexural mode, Mindlin plates theory, which includes the effects of shear deformation and rotatory inertia was shown to give better agreement with the experimental measurements.

Application of Biot Theory to the Study of Acoustic Reflection from Sediments

DTIC Science & Technology

1992-09-08

of bottom loss at all frequencies. To predict propagation loss, a multipath expansion propagation model [15] was used. The sound velocity profile in...public release; distribution unlimited. 13. AISTRACT (Maximum 200 wovov Wave Propagation in fluid-saturated poroelastic media may be described using...of grazing angle and frequency is compared against the more common fluid-fluid and fluid-solid interface models . Finally, shallow water propagation

Southern Africa seismic structure and source studies

NASA Astrophysics Data System (ADS)

Zhao, Ming

1998-09-01

The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data. Waveform and travel time data used in this study come mainly from a large mine tremor in South Africa (msb{b} 5.6) recorded on stations of the southern Africa and the Tanzania Broadband Seismic Experiment. Auxiliary data along similar profiles are obtained from other moderate events within eastern and southern Africa. The waveform data from the large tremor show upper mantle triplications for both the 400 and 670-km discontinuities between 18sp° and 27sp° distance. The most notable feature of the data is a large, late P phase that propagates to at least 27sp°. This phase is striking because of its late arrival time (as much as 15 seconds after direct P at 27sp°) and high amplitude relative to the first arrival. Travel times from all available stations are used to invert for the P wave velocity structure down to 800 km depth and S wave velocity structure down to 200 km using the Wiechert-Herglotz (W-H) inversion technique. The P wave velocities from the uppermost mantle down to 300 km are as much as 3% higher than the global average and are slightly slower than the global average between 300 and 400 km depths. The velocity gradient between 300 and 400 km is 0.0015 1/s. The S wave travel time data yield fast velocities above 200-km depth. The S wave velocity structure appears inconsistent with the P wave structure model indicating varying Poisson's ratio in the upper mantle. Little evidence is found for a pronounced upper mantle low velocity zone. Both sharp and gradual-change 400-km discontinuities are favored by the waveform data. The 670-km discontinuity appears as a gradual-change zone. The source mechanism of the mb 5.6 mining tremor itself is important for seismic discrimination and insight into mining tremor sources. Source parameters for this event as well as some other large mining tremors from the South African gold mines are studied using detailed waveform modeling. All these events (mb > 4.8) indicate normal-faulting slip with P wave nodal planes striking approximately NS. Tectonic stress is essential to control the mining seismicity of large magnitude. Mining geometry also plays an important role in influencing the seismicity. The crustal velocity structure at the study area is investigated in detail using teleseismic receiver function and regional surface wave dispersion data. The results indicate some lateral variation in the shallow crust. The thickness of the crust beneath the GSN station BOSA is 33-36 km. Gradually increasing velocities with depth in the crust are preferred. A thin layer with rather low velocity at the top of the crust beneath BOSA is important for generating the regional waveforms. The crust beneath LBTB is a few kilometers thicker than at BOSA and the Moho there is likely to be dipping. (Abstract shortened by UMI.)

Frictional properties of fault rocks along the shallow part of the Japan Trench décollement: insights from samples recovered during the Integrated Ocean Drilling Project Expedition 343 (the JFAST project)

NASA Astrophysics Data System (ADS)

Remitti, Francesca; Smith, Steven; Gualtieri, Alessandro; Di Toro, Giulio; Nielsen, Stefan

2014-05-01

The Japan Trench Fast Drilling Project (JFAST), Integrated Ocean Drilling Program (IODP) Expedition 343, successfully located and sampled the shallow slip zone of the Mw =9.0 Tohoku-Oki earthquake where the largest coseismic slip occurred (c. 50 m). Logging-while-drilling, core-sample observations and the analysis of temperature data recovered from a third borehole show that a thin (<5 m), smectite rich plate-boundary fault accommodated the large slip of the Tohoku-Oki Earthquake rupture, as well as most of the interplate motion at the drill site. Effective normal stress along the shallow plate-boundary fault is estimated to be c. 7 MPa. Single-velocity and velocity-stepping rotary-shear friction experiments on fault material were performed with the Slow to HIgh Velocity Apparatus (SHIVA) installed at INGV in Rome. Quantitative phase analysis using the combined Rietveld and R.I.R. method indicates that the starting material is mainly composed of smectite (56 wt%) and illite/mica (21 wt%) and minor quartz, kaolinite, plagioclase and K-feldspar. The amount of amorphous fraction has also been calculated and it is close to the detection limit. Each experiment used 3.5 g of loosely disaggregated gouge, following sieving to a particle size fraction <1 mm. Experiments were performed either 1) "room-dry" (40-60% humidity) at 8.5 MPa normal stress (one test at 12.5 MPa), or 2) "water-dampened" (0.5 ml distilled water added to the gouge layers) at 3.5 MPa normal stress. Slip velocities ranged over nearly seven orders of magnitude (10-5 - 3 m s-1). Total displacement is always less than 1 m. The peak and steady-state frictional strengths of the gouges are significantly lower under water-dampened conditions, with mean steady-state friction coefficients (μ, shear stress/normal stress) at all investigated velocities of 0.04<μ<0.1. This is consistent with the small measured frictional heat anomaly along the plate boundary fault ~1.5 years after the Tohoku-Oki earthquake. Under room-dry conditions the gouge material is velocity-strengthening at intermediate velocities (0.001 - 0.1 m s-1), but strongly velocity-weakening at > 0.1 m s-1. Instead, under water-dampened conditions, the gouge is velocity-neutral to velocity-weakening at all investigated velocities. In other words, the intermediate-velocity strengthening, which would probably act as a "barrier" to rupture propagation in the dry gouges, disappears in water-dampened gouges. This result is compatible with propagation of the Tohoku rupture to the trench, and also with large coseismic slip at shallow depths. Quantitative phase analysis using the combined Rietveld and R.I.R. method has been performed also on six post-experiment gouges for the determination of both the crystalline and amorphous fractions. Preliminary results show that the mineralogical assemblage is basically the same after the experiments, with both smectite and illite phases preserved, this suggests that the weakening mechanism operating in this material is active at low temperature.

Seismic evidence for rock damage and healing on the San Andreas fault associated with the 2004 M 6.0 Parkfield earthquake

USGS Publications Warehouse

Li, Y.-G.; Chen, P.; Cochran, E.S.; Vidale, J.E.; Burdette, T.

2006-01-01

We deployed a dense linear array of 45 seismometers across and along the San Andreas fault near Parkfield a week after the M 6.0 Parkfield earthquake on 28 September 2004 to record fault-zone seismic waves generated by aftershocks and explosions. Seismic stations and explosions were co-sited with our previous experiment conducted in 2002. The data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 M 6.0 mainshock show ???1.0%-1.5% decreases in seismic-wave velocity within an ???200-m-wide zone along the fault strike and smaller changes (0.2%-0.5%) beyond this zone, most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 M 6.0 earthquake. The width of the damage zone characterized by larger velocity changes is consistent with the low-velocity waveguide model on the San Andreas fault, near Parkfield, that we derived from fault-zone trapped waves (Li et al., 2004). The damage zone is not symmetric but extends farther on the southwest side of the main fault trace. Waveform cross-correlations for repeated aftershocks in 21 clusters, with a total of ???130 events, located at different depths and distances from the array site show ???0.7%-1.1% increases in S-wave velocity within the fault zone in 3 months starting a week after the earthquake. The velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time, most likely . due to the closure of cracks opened during the mainshock. We estimate that the net decrease in seismic velocities within the fault zone was at least ???2.5%, caused by the 2004 M 6.0 Parkfield earthquake. The healing rate was largest in the earlier stage of the postmainshock healing process. The magnitude of fault healing varies along the rupture zone, being slightly larger for the healing beneath Middle Mountain, correlating well with an area of large mapped slip. The fault healing is most prominent at depths above ???7 km.

Super-alfvenic propagation of cosmic rays: The role of streaming modes

NASA Technical Reports Server (NTRS)

Morrison, P. J.; Scott, J. S.; Holman, G. D.; Ionson, J. A.

1980-01-01

Numerous cosmic ray propagation and acceleration problems require knowledge of the propagation speed of relativistic particles through an ambient plasma. Previous calculations indicated that self-generated turbulence scatters relativistic particles and reduces their bulk streaming velocity to the Alfven speed. This result was incorporated into all currently prominent theories of cosmic ray acceleration and propagation. It is demonstrated that super-Alfvenic propagation is indeed possible for a wide range of physical parameters. This fact dramatically affects the predictions of these models.

Key features of hip hop dance motions affect evaluation by judges.

PubMed

Sato, Nahoko; Nunome, Hiroyuki; Ikegami, Yasuo

2014-06-01

The evaluation of hip hop dancers presently lacks clearly defined criteria and is often dependent on the subjective impressions of judges. Our study objective was to extract hidden motion characteristics that could potentially distinguish the skill levels of hip hop dancers and to examine the relationship between performance kinematics and judging scores. Eleven expert, six nonexpert, and nine novice dancers participated in the study, where each performed the "wave" motion as an experimental task. The movements of their upper extremities were captured by a motion capture system, and several kinematic parameters including the propagation velocity of the wave were calculated. Twelve judges evaluated the performances of the dancers, and we compared the kinematic parameters of the three groups and examined the relationship between the judging scores and the kinematic parameters. We found the coefficient of variation of the propagation velocity to be significantly different among the groups (P < .01) and highly correlated with the judging scores (r = -0.800, P < .01). This revealed that the variation of propagation velocity was the most dominant variable representing the skill level of the dancers and that the smooth propagation of the wave was most closely related to the evaluation by judges.

Superenergy flux of Einstein-Rosen waves

NASA Astrophysics Data System (ADS)

Domínguez, P. J.; Gallegos, A.; Macías-Díaz, J. E.; Vargas-Rodríguez, H.

In this work, we consider the propagation speed of the superenergy flux associated to the Einstein-Rosen cylindrical waves propagating in vacuum and over the background of the gravitational field of an infinitely long mass line distribution. The velocity of the flux is determined considering the reference frame in which the super-Poynting vector vanishes. This reference frame is then considered as comoving with the flux. The explicit expressions for the velocities are given with respect to a reference frame at rest with the symmetry axis.

Vertical amplitude phase structure of a low-frequency acoustic field in shallow water

NASA Astrophysics Data System (ADS)

Kuznetsov, G. N.; Lebedev, O. V.; Stepanov, A. N.

2016-11-01

We obtain in integral and analytic form the relations for calculating the amplitude and phase characteristics of an interference structure of orthogonal projections of the oscillation velocity vector in shallow water. For different frequencies and receiver depths, we numerically study the source depth dependences of the effective phase velocities of an equivalent plane wave, the orthogonal projections of the sound pressure phase gradient, and the projections of the oscillation velocity vector. We establish that at low frequencies in zones of interference maxima, independently of source depth, weakly varying effective phase velocity values are observed, which exceed the sound velocity in water by 5-12%. We show that the angles of arrival of the equivalent plane wave and the oscillation velocity vector in the general case differ; however, they virtually coincide in the zone of the interference maximum of the sound pressure under the condition that the horizontal projections of the oscillation velocity appreciably exceed the value of the vertical projection. We give recommendations on using the sound field characteristics in zones with maximum values for solving rangefinding and signal-detection problems.

Measurement of the velocity of a quantum object: A role of phase and group velocities

NASA Astrophysics Data System (ADS)

Lapinski, Mikaila; Rostovtsev, Yuri V.

2017-08-01

We consider the motion of a quantum particle in a free space. Introducing an explicit measurement procedure for velocity, we demonstrate that the measured velocity is related to the group and phase velocities of the corresponding matter waves. We show that for long distances the measured velocity coincides with the matter wave group velocity. We discuss the possibilities to demonstrate these effects for the optical pulses in coherently driven media or for radiation propagating in waveguides.

40 CFR 146.88 - Injection well operating requirements.

Code of Federal Regulations, 2011 CFR

2011-07-01

..., the owner or operator must ensure that injection pressure does not exceed 90 percent of the fracture pressure of the injection zone(s) so as to ensure that the injection does not initiate new fractures or propagate existing fractures in the injection zone(s). In no case may injection pressure initiate fractures...

40 CFR 146.88 - Injection well operating requirements.

Code of Federal Regulations, 2014 CFR

2014-07-01

..., the owner or operator must ensure that injection pressure does not exceed 90 percent of the fracture pressure of the injection zone(s) so as to ensure that the injection does not initiate new fractures or propagate existing fractures in the injection zone(s). In no case may injection pressure initiate fractures...

40 CFR 146.88 - Injection well operating requirements.

Code of Federal Regulations, 2013 CFR

2013-07-01

..., the owner or operator must ensure that injection pressure does not exceed 90 percent of the fracture pressure of the injection zone(s) so as to ensure that the injection does not initiate new fractures or propagate existing fractures in the injection zone(s). In no case may injection pressure initiate fractures...

40 CFR 146.88 - Injection well operating requirements.

Code of Federal Regulations, 2012 CFR

2012-07-01

..., the owner or operator must ensure that injection pressure does not exceed 90 percent of the fracture pressure of the injection zone(s) so as to ensure that the injection does not initiate new fractures or propagate existing fractures in the injection zone(s). In no case may injection pressure initiate fractures...

Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography: Sound velocities of Iron-rich Oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wicks, June; Jackson, Jennifer M.; Sturhahn, Wolfgang

We explore the effect of Mg/Fe substitution on the sound velocities of iron-rich (Mg 1 - xFe x)O, where x = 0.84, 0.94, and 1.0. Sound velocities were determined using nuclear resonance inelastic X-ray scattering as a function of pressure, approaching those of the lowermost mantle. The systematics of cation substitution in the Fe-rich limit has the potential to play an important role in the interpretation of seismic observations of the core-mantle boundary. By determining a relationship between sound velocity, density, and composition of (Mg,Fe)O, this study explores the potential constraints on ultralow-velocity zones at the core-mantle boundary.

Measuring contraction propagation and localizing pacemaker cells using high speed video microscopy

PubMed Central

Akl, Tony J.; Nepiyushchikh, Zhanna V.; Gashev, Anatoliy A.; Zawieja, David C.; Coté, Gerard L.

2011-01-01

Previous studies have shown the ability of many lymphatic vessels to contract phasically to pump lymph. Every lymphangion can act like a heart with pacemaker sites that initiate the phasic contractions. The contractile wave propagates along the vessel to synchronize the contraction. However, determining the location of the pacemaker sites within these vessels has proven to be very difficult. A high speed video microscopy system with an automated algorithm to detect pacemaker location and calculate the propagation velocity, speed, duration, and frequency of the contractions is presented in this paper. Previous methods for determining the contractile wave propagation velocity manually were time consuming and subject to errors and potential bias. The presented algorithm is semiautomated giving objective results based on predefined criteria with the option of user intervention. The system was first tested on simulation images and then on images acquired from isolated microlymphatic mesenteric vessels. We recorded contraction propagation velocities around 10 mm∕s with a shortening speed of 20.4 to 27.1 μm∕s on average and a contraction frequency of 7.4 to 21.6 contractions∕min. The simulation results showed that the algorithm has no systematic error when compared to manual tracking. The system was used to determine the pacemaker location with a precision of 28 μm when using a frame rate of 300 frames per second. PMID:21361700

Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion Data for Three-Dimensional Seismic Velocity Structure Around SAFOD

NASA Astrophysics Data System (ADS)

Zhang, H.; Thurber, C. H.; Maceira, M.; Roux, P.

2013-12-01

The crust around the San Andreas Fault Observatory at depth (SAFOD) has been the subject of many geophysical studies aimed at characterizing in detail the fault zone structure and elucidating the lithologies and physical properties of the surrounding rocks. Seismic methods in particular have revealed the complex two-dimensional (2D) and three-dimensional (3D) structure of the crustal volume around SAFOD and the strong velocity reduction in the fault damage zone. In this study we conduct a joint inversion using body-wave arrival times and surface-wave dispersion data to image the P-and S-wave velocity structure of the upper crust surrounding SAFOD. The two data types have complementary strengths - the body-wave data have good resolution at depth, albeit only where there are crossing rays between sources and receivers, whereas the surface waves have very good near-surface resolution and are not dependent on the earthquake source distribution because they are derived from ambient noise. The body-wave data are from local earthquakes and explosions, comprising the dataset analyzed by Zhang et al. (2009). The surface-wave data are for Love waves from ambient noise correlations, and are from Roux et al. (2011). The joint inversion code is based on the regional-scale version of the double-difference (DD) tomography algorithm tomoDD. The surface-wave inversion code that is integrated into the joint inversion algorithm is from Maceira and Ammon (2009). The propagator matrix solver in the algorithm DISPER80 (Saito, 1988) is used for the forward calculation of dispersion curves from layered velocity models. We examined how the structural models vary as we vary the relative weighting of the fit to the two data sets and in comparison to the previous separate inversion results. The joint inversion with the 'optimal' weighting shows more clearly the U-shaped local structure from the Buzzard Canyon Fault on the west side of SAF to the Gold Hill Fault on the east side.

Physical exercise counteracts the increase in velocity of propagation of cortical spreading depression imposed by early over-nutrition in rats.

PubMed

Monteiro, Heloísa Mirelle Costa; de Mendonça, Débora Carneiro; Sousa, Mariana Séfora Bezerra; Amancio-Dos-Santos, Angela

2018-06-01

This investigation studied whether physical exercise could modulate cortical spreading depression (CSD) propagation velocity in adult rat offspring from dams that had received a high-fat (HF) diet during lactation. Wistar male rats suckled by dams fed either control (C) or HF diet ad libitum. After weaning, pups received standard laboratory chow. From 40 to 60 days of life, half of the animals exercised on a treadmill (group E); the other half remained sedentary (group S). Two additional HF groups (E and S) received fluoxetine (F; 10 mg/kg/day, orogastrically) from 40 to 60 days of life (groups HF/EF and HF/F). At 40 days of life, rats from the maternal HF diet presented higher weight, thoracic circumference, and Lee Index than C animals and remained heavier at 60 days of life. Physical exercise decreased abdominal circumference. HF diet increased CSD propagation velocity (mean ± SD; mm/min) in sedentaries (HF/S 3.47 ± 0.31 versus C/S 3.24 ± 0.26). Treadmill exercise decelerated CSD propagation in both groups C/E (2.94 ± 0.28) and HF/E (2.97 ± 0.40). Fluoxetine alone decreased CSD propagation (HF/F 2.88 ± 0.45) compared with HF/S group. The combination of fluoxetine + exercise under HF condition (2.98 ± 0.27) was similar to HF/E group. Physical exercise is able to reduce CSD propagation velocity in rat adult brains even when they have suffered over-nourishing during lactation. The effects of exercise alone or fluoxetine alone on CSD were similar to the effects of fluoxetine + exercise, under the HF condition. Data reinforce malnutrition during lactation modifies cortical electrophysiology even when the HF condition no longer exists.

Flying radio frequency undulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuzikov, S. V.; Vikharev, A. A.; Savilov, A. V.

2014-07-21

A concept for the room-temperature rf undulator, designed to produce coherent X-ray radiation by means of a relatively low-energy electron beam and pulsed mm-wavelength radiation, is proposed. The “flying” undulator is a high-power short rf pulse co-propagating together with a relativistic electron bunch in a helically corrugated waveguide. The electrons wiggle in the rf field of the −1st spatial harmonic with the phase velocity directed in the opposite direction in respect to the bunch velocity, so that particles can irradiate high-frequency Compton's photons. A high group velocity (close to the speed of light) ensures long cooperative motion of the particlesmore » and the co-propagating rf pulse.« less

Kramers-Kronig based quality factor for shear wave propagation in soft tissue

PubMed Central

Urban, M W; Greenleaf, J F

2009-01-01

Shear wave propagation techniques have been introduced for measuring the viscoelastic material properties of tissue, but assessing the accuracy of these measurements is difficult for in vivo measurements in tissue. We propose using the Kramers-Kronig relationships to assess the consistency and quality of the measurements of shear wave attenuation and phase velocity. In ex vivo skeletal muscle we measured the wave attenuation at different frequencies, and then applied finite bandwidth Kramers-Kronig equations to predict the phase velocities. We compared these predictions with the measured phase velocities and assessed the mean square error (MSE) as a quality factor. An algorithm was derived for computing a quality factor using the Kramers-Kronig relationships. PMID:19759409

Färoe-Iceland Ridge Experiment: 1. Crustal structure of northeastern Iceland

USGS Publications Warehouse

Staples, Robert K.; White, Robert S.; Brandsdottir, Bryndis; Menke, William; Maguire, Peter K.H.; McBride, John H.

1997-01-01

Results from the Färoe-Iceland Ridge Experiment (FIRE) constrain the crustal thickness as 19 km under the Northern Volcanic Zone of Iceland and 35 km under older Tertiary areas of northeastern Iceland. The Moho is defined by strong P wave and S wave reflections. Synthetic seismogram modeling of the Moho reflection indicates mantle velocities of at least 8.0 km/s beneath the Tertiary areas of northeastern Iceland and at least 7.9 km/s beneath the neovolcanic zone. Crustal diving rays resolve the structure of the upper and lower crust. Surface P wave velocities are 1.1–4.0 km/s in Quaternary rocks and are rather higher, 4.4–4.7 km/s, in the Tertiary basalts that outcrop elsewhere. The highest crustal P wave velocities observed directly from diving rays are 7.1 km/s, from rays that turn at 24 km depth. Velocities of 7.35 km/s at the base of the crust are inferred from extrapolation of the lower crustal velocity gradient (0.024 s−1). A Poisson's ratio of approximately 0.27, equivalent to an S wave to P wave travel time ratio of 1.78, is measured throughout the crust east of the neovolcanic zone. The Poisson's ratio and the steep Moho topography (in places up to 30° from the horizontal) indicate that the entire crust outside the neovolcanic zone is cool (<800°C). Gravity data are well matched by a velocity/density conversion of our seismic crustal model and indicate a region of low mantle density beneath the neovolcanic zone, believed to be due to elevated mantle temperatures. The crustal thickness in the neovolcanic zone is consistent with geochemical estimates of the melt generation, placing constraints on the flow within the Iceland mantle plume.

Seismic Characterization of a Gas Hydrate Chimney Associated with Acoustic Blanking: Pegasus Basin, New Zealand

NASA Astrophysics Data System (ADS)

Henrys, S. A.; Fraser, D. R. A.; Gorman, A. R.; Pecher, I. A.; Crutchley, G. J.

2016-12-01

The Pegasus Basin on the east coast of New Zealand's North Island in the southern part of the Hikurangi Margin is a frontier petroleum basin that is also expected to contain significant gas hydrate deposits. Extensive faulting in the basin has lead to the development of many interesting and unique focused accumulations of gas hydrates. A 2D seismic dataset acquired in 2009/2010 was reprocessed to examine the gas hydrate systems within the basin. Here, we present one of the more interesting hydrate features in the dataset: a presumed gas chimney within the regional gas hydrate stability zone at the centre of a roughly triangular (in 2D) region of low reflectivity, approximately 8 km wide, that is interpreted to be the result of acoustic blanking. Using automated high density velocity picking, the chimney structure is interpreted to be cored by a 200 m wide low-velocity zone which contains free gas and is flanked by high-velocity bands that are 200-400 m wide. The high-velocity zone is interpreted to correspond to concentrated hydrate deposits within the sedimentary pore spaces. Amplitude vs offset (AVO) and inversion techniques have been applied and the results of this work correspond well to the high-density velocity analyses. The analysis methods all indicate zones of free gas below the Bottom Simulating Reflection (BSR) and within the chimney. Areas of increased hydrate concentrations, including at the base of the gas hydrate stability zone, were also identified. A model for fluid flow and how free gas within the chimney at the centre of the blanking zone is converted to hydrate is discussed. The potential size of the gas hydrate resource present in this feature can be estimated based on the seismic velocities and physical properties determined by inversion.

Microplate and shear zone models for oceanic spreading center reorganizations

NASA Technical Reports Server (NTRS)

Engeln, Joseph F.; Stein, Seth; Werner, John; Gordon, Richard

1988-01-01

The kinematics of rift propagation and the resulting goemetries of various tectonic elements for two plates is reviewed with no overlap zone. The formation and evolution of overlap regions using schematic models is discussed. The models are scaled in space and time to approximate the Easter plate, but are simplified to emphasize key elements. The tectonic evolution of overlap regions which act as rigid microplates and shear zones is discussed, and the use of relative motion and structural data to discriminate between the two types of models is investigated. The effect of propagation rate and rise time on the size, shape, and deformation of the overlap region is demonstrated.

The Evolution of Eastern Himalayan Syntaxis of Tibetan Plateau

NASA Astrophysics Data System (ADS)

Zhang, S.; Wu, T.; Li, M.; Zhang, Y.; Hua, Y.; Zhang, B.

2017-12-01

Indian plate has been colliding with Eurasian plate since 50Ma years ago, resulting in the Tethys extinction, crust shortening and Tibetan plateau uplift. But it is still a debate how the Tibetan Plateau material escaped. This study tries to invert the distributions of dispersion phase velocity and anisotropy in Eastern Himalayan Syntaxis (EHS) based on the seismic data. We focused on the seven sub-blocks around EHS region. Sub-block "EHS" represents EHS corner with high velocity anomalies, significantly compressed in the axle and strike directions. Sub-blocks "LSD", "QTB" and "SP-GZB" are located at its northern areas with compressions also, and connected with low-velocity anomalies in both crustal and upper mantle rocks. Sub-block "ICB" is located at its southern area with low velocity anomaly, and connected with Tengchong volcano. Sub-blocks "SYDB" and "YZB" are located at its eastern areas with high velocity anomalies in both crustal and upper mantle rocks. Our results demonstrated that significant azimuthal anisotropy of crust (t£30s) and upper mantle (30s£t£60s). Crustal anisotropy indicates the orogenic belt matched well with the direction of fast propagation, and upper mantle anisotropy represents the lattic-preferred orientation (LPO) of mantle minerals (e.g. olivine and basalt), indicating the features of subducting Indian plate. Besides, Red River fault is a dextral strike fault, controlling the crustal and mantle migration. There is a narrow zone to be the channel flow of Tibetan crustal materials escaping toward Yunnan area. The evolution of EHS seems constrained by gravity isostatic mechanism. Keywords: Tibetan Plateau; Eastern Himalayan Syntaxis; Red River fault; crustal flow; surface wave; anisotropy

Dry granular avalanche impact force on a rigid wall: Analytic shock solution versus discrete element simulations

NASA Astrophysics Data System (ADS)

Albaba, Adel; Lambert, Stéphane; Faug, Thierry

2018-05-01

The present paper investigates the mean impact force exerted by a granular mass flowing down an incline and impacting a rigid wall of semi-infinite height. First, this granular flow-wall interaction problem is modeled by numerical simulations based on the discrete element method (DEM). These DEM simulations allow computing the depth-averaged quantities—thickness, velocity, and density—of the incoming flow and the resulting mean force on the rigid wall. Second, that problem is described by a simple analytic solution based on a depth-averaged approach for a traveling compressible shock wave, whose volume is assumed to shrink into a singular surface, and which coexists with a dead zone. It is shown that the dead-zone dynamics and the mean force on the wall computed from DEM can be reproduced reasonably well by the analytic solution proposed over a wide range of slope angle of the incline. These results are obtained by feeding the analytic solution with the thickness, the depth-averaged velocity, and the density averaged over a certain distance along the incline rather than flow quantities taken at a singular section before the jump, thus showing that the assumption of a shock wave volume shrinking into a singular surface is questionable. The finite length of the traveling wave upstream of the grains piling against the wall must be considered. The sensitivity of the model prediction to that sampling length remains complicated, however, which highlights the need of further investigation about the properties and the internal structure of the propagating granular wave.

Coseismic slip and early afterslip of the 2015 Illapel, Chile, earthquake: Implications for frictional heterogeneity and coastal uplift

USGS Publications Warehouse

Barnhart, William D.; Murray, Jessica R.; Briggs, Richard W.; Gomez, Francisco; Miles, Charles P. J.; Svarc, Jerry L.; Riquelme, Sebástian; Stressler, Bryan J.

2016-01-01

Great subduction earthquakes are thought to rupture portions of the megathrust, where interseismic coupling is high and velocity-weakening frictional behavior is dominant, releasing elastic deformation accrued over a seismic cycle. Conversely, postseismic afterslip is assumed to occur primarily in regions of velocity-strengthening frictional characteristics that may correlate with lower interseismic coupling. However, it remains unclear if fixed frictional properties of the subduction interface, coseismic or aftershock-induced stress redistribution, or other factors control the spatial distribution of afterslip. Here we use interferometric synthetic aperture radar and Global Position System observations to map the distribution of coseismic slip of the 2015 Mw 8.3 Illapel, Chile, earthquake and afterslip within the first 38 days following the earthquake. We find that afterslip overlaps the coseismic slip area and propagates along-strike into regions of both high and moderate interseismic coupling. The significance of these observations, however, is tempered by the limited resolution of geodetic inversions for both slip and coupling. Additional afterslip imaged deeper on the fault surface bounds a discrete region of deep coseismic slip, and both contribute to net uplift of the Chilean Coastal Cordillera. A simple partitioning of the subduction interface into regions of fixed frictional properties cannot reconcile our geodetic observations. Instead, stress heterogeneities, either preexisting or induced by the earthquake, likely provide the primary control on the afterslip distribution for this subduction zone earthquake. We also explore the occurrence of coseismic and postseismic coastal uplift in this sequence and its implications for recent hypotheses concerning the source of permanent coastal uplift along subduction zones.

Collective cell migration without proliferation: density determines cell velocity and wave velocity

NASA Astrophysics Data System (ADS)

Tlili, Sham; Gauquelin, Estelle; Li, Brigitte; Cardoso, Olivier; Ladoux, Benoît; Delanoë-Ayari, Hélène; Graner, François

2018-05-01

Collective cell migration contributes to embryogenesis, wound healing and tumour metastasis. Cell monolayer migration experiments help in understanding what determines the movement of cells far from the leading edge. Inhibiting cell proliferation limits cell density increase and prevents jamming; we observe long-duration migration and quantify space-time characteristics of the velocity profile over large length scales and time scales. Velocity waves propagate backwards and their frequency depends only on cell density at the moving front. Both cell average velocity and wave velocity increase linearly with the cell effective radius regardless of the distance to the front. Inhibiting lamellipodia decreases cell velocity while waves either disappear or have a lower frequency. Our model combines conservation laws, monolayer mechanical properties and a phenomenological coupling between strain and polarity: advancing cells pull on their followers, which then become polarized. With reasonable values of parameters, this model agrees with several of our experimental observations. Together, our experiments and model disantangle the respective contributions of active velocity and of proliferation in monolayer migration, explain how cells maintain their polarity far from the moving front, and highlight the importance of strain-polarity coupling and density in long-range information propagation.

Transient establishment of the wavefronts for negative, zero, and positive refraction.

PubMed

Zhao, Wenjuan; Wu, Qiang; Wang, Ride; Gao, Jianshun; Lu, Yao; Zhang, Qi; Qi, Jiwei; Zhang, Chunling; Pan, Chongpei; Rupp, Romano; Xu, Jingjun

2018-01-22

We quantitatively demonstrate transient establishment of wavefronts for negative, zero, and positive refraction through a wedge-shaped metamaterial consisting of periodically arranged split-ring resonators and metallic wires. The wavefronts for the three types of refractions propagate through the second interface of the wedge along positive refraction angles at first, then reorganize, and finally propagate along the effective refraction angles after a period of establishment time respectively. The establishment time of the wavefronts prevents violating causality or superluminal propagation for negative and zero refraction. The establishment time for negative or zero refraction is longer than that for positive refraction. For all three refraction processes, transient establishment processes precede the establishment of steady propagation. Moreover, some detailed characters are proven in our research, including infinite wavelength, uniform phase inside the zero-index material, and the phase velocity being antiparallel to the group velocity in the negative-index material.

Propagation of atmospheric-pressure ionization waves along the tapered tube

NASA Astrophysics Data System (ADS)

Xia, Yang; Wang, Wenchun; Liu, Dongping; Yan, Wen; Bi, Zhenhua; Ji, Longfei; Niu, Jinhai; Zhao, Yao

2018-02-01

Gas discharge in a small radius dielectric tube may result in atmospheric pressure plasma jets with high energy and density of electrons. In this study, the atmospheric pressure ionization waves (IWs) were generated inside a tapered tube. The propagation behaviors of IWs inside the tube were studied by using a spatially and temporally resolved optical detection system. Our measurements show that both the intensity and velocity of the IWs decrease dramatically when they propagate to the tapered region. After the taper, the velocity, intensity, and electron density of the IWs are improved with the tube inner diameter decreasing from 4.0 to 0.5 mm. Our analysis indicates that the local gas conductivity and surface charges may play a role in the propagation of the IWs under such a geometrical constraint, and the difference in the dynamics of the IWs after the taper can be related to the restriction in the size of IWs.

Analysis of coiled stator ultrasound motor: Fundamental study on analysis of wave propagation on acoustic waveguide for coiled stator

NASA Astrophysics Data System (ADS)

Ozeki, Seiya; Kurita, Keisuke; Uehara, Choyu; Nakane, Noriaki; Sato, Toshio; Takeuchi, Shinichi

2018-07-01

In our research group, we previously developed a coiled stator ultrasound motor (CS-USM) for medical applications such as intravascular ultrasound (IVUS) devices. However, wave propagation on acoustic waveguides has not been investigated sufficiently in previous studies. In this study, we analyze the propagation velocity of elastic waves from the simulated the vibration displacement mode profile along a straight line acoustic waveguide via three-dimensional finite element method (FEM). Concerning results, elastic waves with vibration displacement along the thickness direction show dispersion characteristics corresponding to the a0 and a1 mode plate waves (Lamb waves) in the acoustic waveguide. Our theoretical hypotheses of the propagation velocities were closely borne out by experimental results. We further find that the dispersion characteristic is affected by the width of the acoustic waveguide. We believe that our findings can contribute to improved CS-USM designs for practical application.

Error Propagation Dynamics of PIV-based Pressure Field Calculations: How well does the pressure Poisson solver perform inherently?

PubMed

Pan, Zhao; Whitehead, Jared; Thomson, Scott; Truscott, Tadd

2016-08-01

Obtaining pressure field data from particle image velocimetry (PIV) is an attractive technique in fluid dynamics due to its noninvasive nature. The application of this technique generally involves integrating the pressure gradient or solving the pressure Poisson equation using a velocity field measured with PIV. However, very little research has been done to investigate the dynamics of error propagation from PIV-based velocity measurements to the pressure field calculation. Rather than measure the error through experiment, we investigate the dynamics of the error propagation by examining the Poisson equation directly. We analytically quantify the error bound in the pressure field, and are able to illustrate the mathematical roots of why and how the Poisson equation based pressure calculation propagates error from the PIV data. The results show that the error depends on the shape and type of boundary conditions, the dimensions of the flow domain, and the flow type.

Terahertz generation by relativistic ponderomotive focusing of two co-axial Gaussian laser beams propagating in ripple density plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Subodh; Singh, Ram Kishor, E-mail: ram007kishor@gmail.com; Sharma, R. P.

Terahertz (THz) generation by beating of two co-axial Gaussian laser beams, propagating in ripple density plasma, has been studied when both ponderomotive and relativistic nonlinearities are operative. When the two lasers co-propagate in rippled density plasma, electrons acquire a nonlinear velocity at beat frequency in the direction transverse to the direction of propagation. This nonlinear oscillatory velocity couples with the density ripple to generate a nonlinear current, which in turn generates THz radiation at the difference frequency. The necessary phase matching condition is provided by the density ripple. Relativistic ponderomotive focusing of the two lasers and its effects on yieldmore » of the generated THz amplitude have been discussed. Numerical results show that conversion efficiency of the order of 10{sup −3} can be achieved in the terahertz radiation generation with relativistic ponderomotive focusing.« less

Understanding fast macroscale fracture from microcrack post mortem patterns

PubMed Central

Guerra, Claudia; Scheibert, Julien; Bonamy, Daniel; Dalmas, Davy

2012-01-01

Dynamic crack propagation drives catastrophic solid failures. In many amorphous brittle materials, sufficiently fast crack growth involves small-scale, high-frequency microcracking damage localized near the crack tip. The ultrafast dynamics of microcrack nucleation, growth, and coalescence is inaccessible experimentally and fast crack propagation was therefore studied only as a macroscale average. Here, we overcome this limitation in polymethylmethacrylate, the archetype of brittle amorphous materials: We reconstruct the complete spatiotemporal microcracking dynamics, with micrometer/nanosecond resolution, through post mortem analysis of the fracture surfaces. We find that all individual microcracks propagate at the same low, load-independent velocity. Collectively, the main effect of microcracks is not to slow down fracture by increasing the energy required for crack propagation, as commonly believed, but on the contrary to boost the macroscale velocity through an acceleration factor selected on geometric grounds. Our results emphasize the key role of damage-related internal variables in the selection of macroscale fracture dynamics. PMID:22203962

An artificial stress asperity for initialization of spontaneous rupture propagation - a parametric study of a dynamic model with linear slip-weakening friction

NASA Astrophysics Data System (ADS)

Galis, M.; Pelties, C.; Kristek, J.; Moczo, P.

2012-04-01

Artificial procedures are used to initiate spontaneous rupture on faults with the linear slip-weakening (LSW) friction law. Probably the most frequent technique is the stress asperity. It is important to minimize effects of the artificial initialization on the phase of the spontaneous rupture propagation. The effects may strongly depend on the geometry and size of the asperity, spatial distribution of the stress in and around the asperity, and a maximum stress-overshoot value. A square initialization zone with the stress discontinuously falling down at the asperity border to the level of the initial stress has been frequently applied (e.g., in the SCEC verification exercise). Galis et al. (2010) and Bizzarri (2010) independently introduced the elliptical asperity with a smooth spatial stress distribution in and around the asperity. In both papers the width of smoothing/tapering zone was only ad-hoc defined. Numerical simulations indicate that the ADER-DG method can account for a discontinuous-stress initialization more accurately than the FE method. Considering the ADER-DG solution a reference we performed numerical simulations in order to define the width of the smoothing/tapering zone to be used in the FE and FD-FE hybrid methods for spontaneous rupture propagation. We considered different sizes of initialization zone, different shapes of the initialization zone (square, circle, ellipse), different spatial distributions of stress (smooth, discontinuous), and different stress-overshoot values to investigate conditions of the spontaneous rupture propagation. We compare our numerical results with the 2D and 3D estimates by Andrews (1976a,b), Day (1982), Campillo & Ionescu (1997), Favreau at al. (1999) and Uenishi & Rice (2003, 2004). Results of our study may help modelers to better setup the initialization zone in order to avoid, e.g., a too large initialization zone and reduce numerical artifacts.

The velocity field of a coronal mass ejection - The event of September 1, 1980

NASA Technical Reports Server (NTRS)

Low, B. C.; Hundhausen, A. J.

1987-01-01

The velocity field of a mass ejection that was observed by the coronagraph of the SMM satellite over the northwest limb of the sun at about 0600 UT on September 1, 1980 is studied in detail. A descriptive account of the event is given, concentrating on qualitative features of the mass motion and suggesting a possible origin of the unusual two-loop structure. The velocity field is analyzed quantitatively, and the implications of the results for the mass ejection theory are considered. It is concluded that a self-similar description of the velocity field is a gross oversimplification and that although some evidence of wave propagation can be found, the bright features in the mass ejection are plasma structures moving with frozen-in magnetic fields, rather than waves propagating through plasmas and magnetic fields.

Nonlinear pulse propagation and phase velocity of laser-driven plasma waves

NASA Astrophysics Data System (ADS)

Benedetti, Carlo; Rossi, Francesco; Schroeder, Carl; Esarey, Eric; Leemans, Wim

2014-10-01

We investigate and characterize the laser evolution and plasma wave excitation by a relativistically intense, short-pulse laser propagating in a preformed parabolic plasma channel, including the effects of pulse steepening, frequency redshifting, and energy depletion. We derived in 3D, and in the weakly relativistic intensity regime, analytical expressions for the laser energy depletion, the pulse self-steepening rate, the laser intensity centroid velocity, and the phase velocity of the plasma wave. Analytical results have been validated numerically using the 2D-cylindrical, ponderomotive code INF&RNO. We also discuss the extension of these results to the nonlinear regime, where an analytical theory of the nonlinear wake phase velocity is lacking. Work supported by the Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Vortex Rossby Waves in Asymmetric Basic Flow of Typhoons

NASA Astrophysics Data System (ADS)

Wang, Tianju; Zhong, Zhong; Wang, Ju

2018-05-01

Wave ray theory is employed to study features of propagation pathways (rays) of vortex Rossby waves in typhoons with asymmetric basic flow, where the tangential asymmetric basic flow is constructed by superimposing the wavenumber-1 perturbation flow on the symmetric basic flow, and the radial basic flow is derived from the non-divergence equation. Results show that, in a certain distance, the influences of the asymmetry in the basic flow on group velocities and slopes of rays of vortex Rossby waves are mainly concentrated near the radius of maximum wind (RMW), whereas it decreases outside the RMW. The distributions of radial and tangential group velocities of the vortex Rossby waves in the asymmetric basic flow are closely related to the azimuth location of the maximum speed of the asymmetric basic flow, and the importance of radial and tangential basic flow on the group velocities would change with radius. In addition, the stronger asymmetry in the basic flow always corresponds to faster outward energy propagation of vortex Rossby waves. In short, the group velocities, and thereby the wave energy propagation and vortex Rossby wave ray slope in typhoons, would be changed by the asymmetry of the basic flow.

Stochastic simulation for the propagation of high-frequency acoustic waves through a random velocity field

NASA Astrophysics Data System (ADS)

Lu, B.; Darmon, M.; Leymarie, N.; Chatillon, S.; Potel, C.

2012-05-01

In-service inspection of Sodium-Cooled Fast Reactors (SFR) requires the development of non-destructive techniques adapted to the harsh environment conditions and the examination complexity. From past experiences, ultrasonic techniques are considered as suitable candidates. The ultrasonic telemetry is a technique used to constantly insure the safe functioning of reactor inner components by determining their exact position: it consists in measuring the time of flight of the ultrasonic response obtained after propagation of a pulse emitted by a transducer and its interaction with the targets. While in-service the sodium flow creates turbulences that lead to temperature inhomogeneities, which translates into ultrasonic velocity inhomogeneities. These velocity variations could directly impact the accuracy of the target locating by introducing time of flight variations. A stochastic simulation model has been developed to calculate the propagation of ultrasonic waves in such an inhomogeneous medium. Using this approach, the travel time is randomly generated by a stochastic process whose inputs are the statistical moments of travel times known analytically. The stochastic model predicts beam deviations due to velocity inhomogeneities, which are similar to those provided by a determinist method, such as the ray method.

Particle-in-cell Simulations of Waves in a Plasma Described by Kappa Velocity Distribution as Observed in the Saturńs Magnetosphere

NASA Astrophysics Data System (ADS)

Alves, M. V.; Barbosa, M. V. G.; Simoes, F. J. L., Jr.

2016-12-01

Observations have shown that several regions in space plasmas exhibit non-Maxwellian distributions with high energy superthermal tails. Kappa velocity distribution functions can describe many of these regions and have been used since the 60's. They suit well to represent superthermal tails in solar wind as well as to obtain plasma parameters of plasma within planetary magnetospheres. A set of initial velocities following kappa distribution functions is used in KEMPO1 particle simulation code to analyze the normal modes of wave propagation. Initial conditions are determined using observed characteristics for Saturńs magnetosphere. Two electron species with different temperatures and densities and ions as a third species are used. Each electron population is described by a different kappa index. Particular attention is given to perpendicular propagation, Bernstein modes, and parallel propagation, Langmuir and electron-acoustic modes. The dispersion relation for the Bernstein modes is strongly influenced by the shape of the velocity distribution and consequently by the value of kappa index. Simulation results are compared with numerical solutions of the dispersion relation obtained in the literature and they are in good agreement.

Imaging two-dimensional mechanical waves of skeletal muscle contraction.

PubMed

Grönlund, Christer; Claesson, Kenji; Holtermann, Andreas

2013-02-01

Skeletal muscle contraction is related to rapid mechanical shortening and thickening. Recently, specialized ultrasound systems have been applied to demonstrate and quantify transient tissue velocities and one-dimensional (1-D) propagation of mechanical waves during muscle contraction. Such waves could potentially provide novel information on musculoskeletal characteristics, function and disorders. In this work, we demonstrate two-dimensional (2-D) mechanical wave imaging following the skeletal muscle contraction. B-mode image acquisition during multiple consecutive electrostimulations, speckle-tracking and a time-stamp sorting protocol were used to obtain 1.4 kHz frame rate 2-D tissue velocity imaging of the biceps brachii muscle contraction. The results present novel information on tissue velocity profiles and mechanical wave propagation. In particular, counter-propagating compressional and shear waves in the longitudinal direction were observed in the contracting tissue (speed 2.8-4.4 m/s) and a compressional wave in the transverse direction of the non-contracting muscle tissue (1.2-1.9 m/s). In conclusion, analysing transient 2-D tissue velocity allows simultaneous assessment of both active and passive muscle tissue properties. Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Possible Different Rifting Mechanisms Between South and North Part of the Fenhe-Weihe Rift Zone Revealed by Shear Velocity Structures

NASA Astrophysics Data System (ADS)

Ai, S.; Zheng, Y.

2017-12-01

As an active intraplate continental rift, FWR plays an important role in accommodating the trans-tension in the Trans North China Craton (TNCO). Velocity field derived from GPS measurements reveals that the northern part of FWR is still under extension in N105°E direction at a rate of 4±2 mm/yr [Shen et al., 2000]. Actually, the FWR has been the most seismically active region in NCC. Bouguer gravity profile and seismic sounding lines [Xu and Ma, 1992] revealed a 2-3 km uplift of Moho depth beneath Taiyuan basin and 5-6 km beneath the Southwestern rift zone, those geophysical observations give clues to the un-evenly upwelling of the asthenosphere beneath the rift system and the different rifting process of the FWR. Therefore, studying the extension process of FWR is meaningful to understanding the NCC geodynamics associated with rifting tectonism. Using vertical continuous waveforms recorded during 2014 from CEarray, we construct a reliable and detailed 3-D crustal and uppermost mantle S-wave velocity structure of FWR, using a Bayesian Monte-Carlo method to jointly interpret teleseismic P-wave receiver functions and Rayleigh wave dispersions [Shen et al., 2013]. In the upmost crust, FWR appear as awful low velocity anomaly zone (LVZ), while the Taihang and Lvliang mountain ranges are imaged as strong high velocity anomaly zones(HVZ). In the middle crust, the low velocity zones still keep their LVZ features Additionally, nearly the whole FWR appears as a linearly LVZ line separating Taihang Uplift and Lvliang Uplift, except beneath Shilingguan and Linshi blocks that separate the Xinxian, Taiyuan and Linfen Basins, consisting with the high seismicity there. The velocity of the lower crust beneath Taiyuan and Weihe Basin are relatively higher than the rest rift regions, we interpret them as the limited mafic underplating beneath the TNCO. From the lower crust to upper mantle, the Datong volcanic zone display robust low velocity features, though the lowest velocity location varies as depth changes. Associated with previous geochemistry studies, we propose an on-going asthenosphere upwelling near Datong volcanic field. Overall, the shear wave velocity structures between north and south part of the FWR is different,and imply the different rifting mechanisms between the two sides of FWR.

Creeping Guanxian-Anxian Fault ruptured in the 2008 Mw 7.9 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

He, X.; Li, H.; Wang, H.; Zhang, L.; Si, J.

2017-12-01

Crustal active faults can slide either steadily by aseismic creep, or abruptly by earthquake rupture. Creep can relax continuously the stress and reduce the occurrence of large earthquakes. Identifying the behaviors of active faults plays a crucial role in predicting and preventing earthquake disasters. Based on multi-scale structural analyses for fault rocks from the GAF surface rupture zone and the Wenchuan Earthquake Fault Zone Science Drilling borehole 3P, we detect the analogous "mylonite structures" develop pervasively in GAF fault rocks. Such specious "ductile deformations", showing intensive foliation, spindly clasts, tailing structure, "boudin structure", "augen structure" and S-C fabrics, are actually formed in brittle faulting, which indicates the creeping behavior of the GAF. Furthermore, some special structures hint the creeping mechanism. The cracks and veins developed in fractured clasts imply pressure and fluid control in the faulting. Under the effect of fluid, clasts are dissolved in pressing direction, and solutions are transferred to stress vacancy area at both ends of clasts and deposit to regenerate clay minerals. The clasts thus present spindly shape and are surrounded by orientational clay minerals constituting continuous foliation structure. The clay minerals are dominated by phyllosilicates that can weaken faults and promote pressure solution. Therefore, pressure solution creep and phyllosilicates weakening reasonably interpret the creeping of GAF. Additionally, GPS velocity data show slip rates of the GAF are respectively 1.5 and 12 mm/yr during 1998-2008 and 2009-2011, which also indicate the GAF is in creeping during interseismic period. According to analysis on aftershocks distribution and P-wave velocity with depth and geological section in the Longmenshan thrust belt, we suggest the GAF is creeping in shallow (<10 km) and locked in deep (10-20 km). Comprehensive research shows stress propagated from the west was concentrated near the Yingxiu-Beichuan Fault (YBF) and GAF zones. As stress accumulation reached the limit, the YBF and GAF zones were simultaneously ruptured in 2008 Mw 7.9 Wenchuan earthquake, but the rupture area of the GAF was relatively small due to the presence of shallow creep that relaxed the partial stress.

In-Plane Ultrasound Propagation in an Elastic Silicone Tube as a Function of Tension

NASA Astrophysics Data System (ADS)

Rajakenttä, Tina; Salmi, Ari; Akujärvi, Altti; Haapalainen, Jonne; Hæggström, Edward

2007-03-01

The mechanical properties of a silicone tube blood vessel phantom (outer radius 4.04±0.04 mm and wall thickness 1.00±0.02 mm) carrying in-plane ultrasound wave propagation, was studied as function of applied axial tension. A 23 kHz, 1-cycle square signal was excited into the tube with a piezoceramic pickup and received with an inductive pickup. The wave phase velocities in the tube were determined by measuring the time-of-flight (TOF) at different inter-transducer distances. The longitudinal mode sound velocity ranged from 83 m/s to 88 m/s, and from 51 m/s to 58 m/s for the shear mode respectively with tensions ranging from 31 to 364 kPa. This compares with the FEM estimate. A laser-Doppler vibrometer (LDV) detected an out-of-plane mode propagating along the tube. An increase in the sound velocity caused by artificially induced lesions was detected.

Envelope matching for enhanced backward Raman amplification by using self-ionizing plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Z. M.; Zhang, B.; Hong, W.

2014-12-15

Backward Raman amplification (BRA) in plasmas has been promoted as a means for generating ultrapowerful laser pulses. For the purpose of achieving the maximum intensities over the shortest distances, an envelope matching between the seed pulse and the amplification gain is required, i.e., the seed pulse propagates at the same velocity with the gain such that the peak of the seed pulse can always enjoy the maximum gain. However, such an envelope matching is absent in traditional BRA because in the latter the amplification gain propagates at superluminous velocity while the seed pulse propagates at the group velocity, which ismore » less than the speed of light. It is shown here that, by using self-ionizing plasmas, the speed of the amplification gain can be well reduced to reach the envelope matching regime. This results in a favorable BRA process, in which higher saturated intensity, shorter interaction length and higher energy-transfer efficiency are achieved.« less

Mantle viscosity beneath the Galapagos 95.5 deg W propagating rift

NASA Technical Reports Server (NTRS)

Schubert, G.; Hey, R. N.

1986-01-01

Detailed geophysical surveys in the vicinity of the Galapagos 95.5 deg W propagating rift tip establish the opening history of the rift and its velocity of propagation. These data together with a theory for mantle upwelling into slowly widening lithospheric cracks constrain the viscosity of the asthenosphere beneath the propagating rift to be less than about 10 to the 17th to 10 to the 18th Pa s.

Discharge mode transition and temporal-spatial evolution of an air-water plasma jet generated by pulsating DC power

NASA Astrophysics Data System (ADS)

Lei, J.; Geng, Y.; Liu, K.; Zhu, W.; Zheng, Z.; Hu, H.

2017-12-01

In this paper, pulsating direct current air-water plasma jet, which can increase the production of •OH and decrease the temperature, is studied. The results show that the discharge mode changes in one cycle from corona discharge with steep Trichel current pulse to glow-like discharge. It is unknown whether the different discharge modes and water ratio have an effect on the transient process of the excited O and •OH production and the mechanism of plasma propagation. So, a series of experiments are done in this paper. The results show that the changing rules of both the excited state O and the discharge current reach their two peak values synchronously. And its maximum appears at the time of the first peak current value in corona mode. However, the change of the excited state •OH is different. It increases to its maximum at the time of the second peak current value in glow-like mode. Besides, the intensified charge coupled device photographs show that the luminous intensity of the discharge zone at the first peak current value in corona mode is stronger than the second peak current value in glow-like mode. At the same time, the discharge area of the former is larger than the latter. Nevertheless, with the increase in water ratio, the discharge area change reversed. Additionally, the air plasma plume propagation depends on the gas flow. The initial propagation velocity decreases with the increase in water ratio.

Effect of Aluminium Confinement on ANFO Detonation

NASA Astrophysics Data System (ADS)

Short, Mark; Jackson, Scott; Kiyanda, Charles; Shinas, Mike; Hare, Steve; Briggs, Matt

2013-06-01

Detonations in confined non-ideal high explosives often have velocities below the confiner sound speed. The effect on detonation propagation of the resulting subsonic flow in the confiner (such as confiner stress waves traveling ahead of the main detonation front or upstream wall deflection into the HE) has yet to be fully understood. Previous work by Sharpe and Bdzil (J. Eng. Math, 2006) has shown that for subsonic confiner flow, there is no limiting thickness for which the detonation dynamics are uninfluenced by further increases in wall thickness. The critical parameters influencing detonation behavior are the wall thickness relative to the HE reaction zone size, and the difference in the detonation velocity and confiner sound speed. Additional possible outcomes of subsonic flow are that for increasing thickness, the confiner is increasingly deflected into the HE upstream of the detonation, and that for sufficiently thick confiners, the detonation speed could be driven up to the sound speed in the confiner. We report here on a further series of experiments in which a mixture of ammonium nitrate and fuel oil (ANFO) is detonated in aluminum confiners with varying HE charge diameter and confiner thickness, and compare the results with the outcomes suggested by Sharpe and Bdzil.

Nonideal detonation regimes in low density explosives

NASA Astrophysics Data System (ADS)

Ershov, A. P.; Kashkarov, A. O.; Pruuel, E. R.; Satonkina, N. P.; Sil'vestrov, V. V.; Yunoshev, A. S.; Plastinin, A. V.

2016-02-01

Measurements using Velocity Interferometer System for Any Reflector (VISAR) were performed for three high explosives at densities slightly above the natural loose-packed densities. The velocity histories at the explosive/window interface demonstrate that the grain size of the explosives plays an important role. Fine-grained materials produced rather smooth records with reduced von Neumann spike amplitudes. For commercial coarse-grained specimens, the chemical spike (if detectable) was more pronounced. This difference can be explained as a manifestation of partial burn up. In fine-grained explosives, which are more sensitive, the reaction can proceed partly within the compression front, which leads to a lower initial shock amplitude. The reaction zone was shorter in fine-grained materials because of higher density of hot spots. The noise level was generally higher for the coarse-grained explosives, which is a natural stochastic effect of the highly non-uniform flow of the heterogeneous medium. These results correlate with our previous data of electrical conductivity diagnostics. Instead of the classical Zel'dovich-von Neumann-Döring profiles, violent oscillations around the Chapman-Jouguet level were observed in about half of the shots using coarse-grained materials. We suggest that these unusual records may point to a different detonation wave propagation mechanism.

Geological structure analysis in Central Java using travel time tomography technique of S waves

NASA Astrophysics Data System (ADS)

Palupi, I. R.; Raharjo, W.; Nurdian, S. W.; Giamboro, W. S.; Santoso, A.

2016-11-01

Java is one of the islands in Indonesia that is prone to the earthquakes, in south of Java, there is the Australian Plate move to the Java island and press with perpendicular direction. This plate movement formed subduction zone and cause earthquakes. The earthquake is the release of energy due to the sudden movement of the plates. When an earthquake occurs, the energy is released and record by seismometers in the waveform. The first wave recorded is called the P waves (primary) and the next wave is called S waves (secondary). Both of these waves have different characteristics in terms of propagation and direction of movement. S wave is composed of waves of Rayleigh and Love waves, with each direction of movement of the vertical and horizontal, subsurface imaging by using S wave tomography technique can describe the type of the S wave through the medium. The variation of wave velocity under Central Java (esearch area) is ranging from -10% to 10% at the depth of 20, 30 and 40 km, the velocity decrease with the depth increase. Moho discontinuity is lies in the depth of 32 km under the crust, it is indicates there is strong heterogenity in Moho.

Time-evolution of uniform momentum zones in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Laskari, Angeliki; Hearst, R. Jason; de Kat, Roeland; Ganapathisubramani, Bharathram

2016-11-01

Time-resolved planar particle image velocimetry (PIV) is used to analyse the organisation and evolution of uniform momentum zones (UMZs) in a turbulent boundary layer. Experiments were performed in a recirculating water tunnel on a streamwise-wall-normal plane extending approximately 0 . 5 δ × 1 . 8 δ , in x and y, respectively. In total 400,000 images were captured and for each of the resulting velocity fields, local peaks in the probability density distribution of the streamwise velocity were detected, indicating the instantaneous presence of UMZs throughout the boundary layer. The main characteristics of these zones are outlined and more specifically their velocity range and wall-normal extent. The variation of these characteristics with wall normal distance and total number of zones are also discussed. Exploiting the time information available, time-scales of zones that have a substantial coherence in time are analysed and results show that the zones' lifetime is dependent on both their momentum deficit level and the total number of zones present. Conditional averaging of the flow statistics seems to further indicate that a large number of zones is the result of a wall-dominant mechanism, while the opposite implies an outer-layer dominance.

Effects of fault dip and slip rake angles on near-source ground motions: Why rupture directivity was minimal in the 1999 Chi-Chi, Taiwan, earthquake

USGS Publications Warehouse

Aagaard, Brad T.; Hall, J.F.; Heaton, T.H.

2004-01-01

We study how the fault dip and slip rake angles affect near-source ground velocities and displacements as faulting transitions from strike-slip motion on a vertical fault to thrust motion on a shallow-dipping fault. Ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip. The nature of the shear-wave directivity is the key factor in determining the size and distribution of the peak velocities and displacements. Strong shear-wave directivity requires that (1) the observer is located in the direction of rupture propagation and (2) the rupture propagates parallel to the direction of the fault slip vector. We show that predominantly along-strike rupture of a thrust fault (geometry similar in the Chi-Chi earthquake) minimizes the area subjected to large-amplitude velocity pulses associated with rupture directivity, because the rupture propagates perpendicular to the slip vector; that is, the rupture propagates in the direction of a node in the shear-wave radiation pattern. In our simulations with a shallow hypocenter, the maximum peak-to-peak horizontal velocities exceed 1.5 m/sec over an area of only 200 km2 for the 30??-dipping fault (geometry similar to the Chi-Chi earthquake), whereas for the 60??- and 75??-dipping faults this velocity is exceeded over an area of 2700 km2 . These simulations indicate that the area subjected to large-amplitude long-period ground motions would be larger for events of the same size as Chi-Chi that have different styles of faulting or a deeper hypocenter.